Astronomy of observation. Sections of observational astronomy. Structure and scale of the universe

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The sun, moon, planets, comets, stars, nebulae, galaxies, individual celestial bodies and systems of such bodies are studied in astronomy. The tasks facing astronomers are varied, and in connection with this, the methods of astronomical observations, which provide the basic material for solving these problems, are also diverse.

Already in ancient times, observations began to determine the positions of the luminaries in the celestial sphere. Now astrometry is doing it. The celestial coordinates of stars of various types, star clusters, and galaxies measured as a result of such observations are cataloged, and star charts are compiled from them (see Star catalogs, maps and atlases). By repeating observations of the same celestial bodies for a more or less long period of time, the proper motions of stars, trigonometric parallaxes, etc. are calculated. These data are also published in catalogs.

Star catalogs compiled in this way are used both for practical purposes - in astronomical observations of moving celestial bodies (planets, comets, artificial space objects), in the work of the time service, the service of the movement of the poles, in geodesy, navigation, etc., and in various kinds of scientific -research work. The latter include, in particular, studies of the structure of the Galaxy, the movements occurring in it, which is what stellar astronomy deals with.

Systematic astrometric observations of planets, comets, asteroids, and artificial space objects provide material for studying the laws of their motion, compiling ephemeris, and solving other problems of celestial mechanics, astrodynamics, geodesy, and gravimetry.

Astrometric observations can also include range-finding observations of celestial bodies that have come into practice in recent decades. With the help of laser range finders, the distances to artificial satellites of the Earth (see Laser satellite range finder) and to the Moon are determined with high accuracy.

Radar astronomy methods make it possible to determine distances and even study the profiles of the Moon, Venus, Mercury, etc.

Another type of astronomical observation is the direct study of the appearance of such celestial bodies as the Sun, the Moon, the nearest planets, galactic nebulae, galaxies, etc. Observations of this type began to develop after the invention of the telescope. Initially, observations were carried out visually: the heavenly bodies were examined by the eye and what was seen was sketched. Later, photography began to be used. Photographic methods have an undeniable advantage over visual methods: photographs can be measured in detail in a calm laboratory environment; if necessary, they can be repeated, and in general a photograph is an objective document, while an observer introduces a lot of subjectivity into visual observations. In addition, a photographic plate, unlike the eye, accumulates photons coming from a source and therefore makes it possible to take pictures of faint objects.

At the turn of the XIX and XX centuries. astrophysical methods of observation were born and began to develop rapidly, based on the analysis of the electromagnetic radiation of the celestial body collected by the telescope. For this analysis, various light detectors and other devices are used.

With the help of various types of astrophotometers, changes in the brightness of celestial bodies are recorded and in this way variable stars are detected, determining their type, double stars, in combination with the results of other observations, certain conclusions are made about the processes occurring in stars, nebulae, etc.

Spectral observations provide extensive information about celestial bodies. According to the distribution of energy in the continuous spectrum (see Electromagnetic radiation of celestial bodies), according to the type, width and other characteristics of the spectral lines and bands, they judge the temperature, the chemical composition of stars and other celestial bodies, the movements of matter in them, their rotation, the presence magnetic fields, finally, about the stage of their evolutionary development and about many other things. Measurements of the shift of spectral lines due to the Doppler effect make it possible to determine the radial velocities of celestial bodies, which are used in various astronomical studies.

In astrophysical observations, electron-optical converters, photomultipliers, electronic cameras, and television equipment (see Television telescope) are widely used, which make it possible to significantly increase the penetrating power of telescopes and expand the range of electromagnetic radiation of celestial bodies perceived by the telescope.

Astronomical observations in the radio range of electromagnetic radiation are carried out with the help of radio telescopes. Special equipment is used to register infrared and ultraviolet radiation, for the needs of x-ray astronomy and gamma-ray astronomy. Qualitatively new results are obtained with the help of astronomical observations carried out on board spacecraft (the so-called extra-atmospheric astronomy).

Most of the described astronomical observations are carried out at astronomical observatories by specially trained scientists and technicians. But certain types of observations are also available to astronomy lovers.

Young astronomers can make observations to broaden their horizons, to gain experience in research work. But many kinds of well-organized observations, carried out in strict accordance with the instructions, can also be of significant scientific value.

The following astronomical observations are available to scale astronomical circles:

1. Study of solar activity using a school refractor telescope (remember that you should never look at the Sun without a dark filter!).

2. Observations of Jupiter and its satellites with a sketch of details in the bands of Jupiter, the Red Spot.

3. Search for comets using high-aperture optical instruments with a sufficiently large field of view.

4. Observations of noctilucent clouds, studying the frequency of their appearance, shape, etc.

5. Registration of meteors, counting their number, determination of radiants.

6. Studies of variable stars - visually and in photographs of the starry sky.

7. Observations of solar and lunar eclipses.

8. Observations of artificial earth satellites.

Instructions for organizing observations can be found among the books listed in the list of recommended reading. A number of practical tips are given in the section.

1. Astronomy is a new discipline in the course, although you are familiar with some of the topics in a nutshell.
2. What do you need:

1. Textbook: . Astronomy. Basic level.11 grade: textbook / B.A. Vorontsov-Velyaminov, E.K. Strout - 5th ed., revised .- M .: Bustard, 2018.-238s, with: ill., 8 sheets. col. incl. - (Russian textbook).;
2. general notebook - 48 sheets.

1. How to work with the textbook.

• work through (rather than read) a paragraph
• to delve into the essence, to deal with each phenomenon and process
• work through all the questions and tasks after the paragraph, briefly in notebooks
• check your knowledge on the list of questions at the end of the topic
• see additional material on the Internet

Topic 1.1 The subject of astronomy. Observations are the basis of astronomy.

1.1.1 What does astronomy study. Its significance and connection with other sciences

Astronomy is one of the oldest sciences, the origins of which date back to the Stone Age (VI-III millennium BC).

Astronomy it is a science that studies the movement, structure, origin and development of celestial bodies and their systems.

Astronomy[Greek Astron (astron) - star, nomos (nomos) - law] - a science that studies the movement of celestial bodies (section "celestial mechanics"), their nature (section "astrophysics"), origin and development (section "cosmogony")

Astronomy, one of the most fascinating and ancient sciences of nature, explores not only the present, but also the distant past of the macroworld around us, and also allows us to draw a scientific picture of the future of the Universe. Man has always been interested in the question of how the world around him works and what place he occupies in it. At the dawn of civilization, most peoples had special cosmological myths that tell how space (order) gradually arises from the initial chaos, everything that surrounds a person appears: heaven and earth, mountains, seas and rivers, plants and animals, as well as the person himself. For thousands of years there has been a gradual accumulation of information about the phenomena that took place in the sky.

The need for astronomical knowledge was dictated by vital necessity (demonstration of films: " All the secrets of space #21 - Discovery - the history of astronomy" and Astronomy (2⁄15). The oldest science.)

It turned out that periodic changes in terrestrial nature are accompanied by changes in the appearance of the starry sky and the apparent movement of the Sun. It was necessary to calculate the onset of a certain time of the year in order to carry out certain agricultural work on time: sowing, watering, harvesting. But this could only be done using a calendar compiled from long-term observations of the position and movement of the Sun and Moon. So the need for regular observations of celestial bodies was due to the practical needs of counting time. The strict periodicity inherent in the movement of heavenly bodies underlies the basic units of time counting that are still used today - day, month, year.

Simple contemplation of occurring phenomena and their naive interpretation were gradually replaced by attempts to scientifically explain the causes of observed phenomena. When in Ancient Greece (VI century BC) the rapid development of philosophy as a science of nature began, astronomical knowledge became an integral part of human culture. Astronomy is the only science that has received its patron muse - Urania.

On the initial significance of the development of astronomical knowledge can be judged in connection with the practical needs of people. They can be divided into several groups:

• agricultural needs(the need for counting time is days, months, years. For example, in ancient Egypt, the time of sowing and harvesting was determined by the appearance before sunrise from behind the edge of the horizon of the bright star Sothis, a harbinger of the Nile flood);
• trade expansion needs, including marine (seafaring, searching for trade routes, navigation. So, the Phoenician sailors were guided by the North Star, which the Greeks called the Phoenician Star);
• aesthetic and cognitive needs, the need for a holistic worldview(man sought to explain the periodicity of natural phenomena and processes, the emergence of the surrounding world).

The origin of astronomy in astrological ideas is characteristic of the mythological worldview of ancient civilizations.

I-th Antique world(BC). Philosophy →astronomy → elements of mathematics (geometry). Ancient Egypt, Ancient Assyria, Ancient Maya, Ancient China, Sumerians, Babylonia, Ancient Greece.

Scientists who have made a significant contribution to the development of astronomy: Thales of Miletus(625-547, Dr. Greece), Eudox of Knidos(408-355, Other Greece), ARISTOTLE(384-322, Macedonia, Other Greece), Aristarchus of Samos(310-230, Alexandria, Egypt), ERATOSPHENES(276-194, Egypt), Hipparchus of Rhodes(190-125, Ancient Greece).

Archaeologists have established that man possessed basic astronomical knowledge already 20 thousand years ago in the Stone Age.

• Prehistoric stage from 25 thousand years BC to 4 thousand BC (rock paintings, natural observatories, etc.).
• The ancient stage can conditionally be considered from 4,000 years BC-1000 BC:
  • about 4 thousand BC astronomical monuments of the ancient Maya, Stonehenge stone observatory (England);
  • about 3000 BC orientation of the pyramids, the first astronomical records in Egypt, Babylon, China;
  • around 2500 BC establishment of the Egyptian solar calendar;
  • around 2000 BC creation of the 1st sky map (China);
  • about 1100 BC determination of the inclination of the ecliptic to the equator;
• antique stage
  • ideas about the sphericity of the Earth (Pythagoras, 535 BC);
  • the prediction of a solar eclipse by Thales of Miletus (585 BC);
  • the establishment of a 19-year cycle of lunar phases (Metonic cycle, 433 BC);
  • ideas about the rotation of the Earth around its axis (Heraclitus of Pontus, 4th century BC);
  • the idea of ​​concentric circles (Eudoxus), the treatise "On the Sky" Aristotle (proof of the sphericity of the Earth and planets) compilation of the first catalog of stars 800 stars, China (4th century BC);
  • the beginning of systematic determinations of the positions of stars by Greek astronomers, the development of the theory of the system of the world (3rd century BC);
  • discovery of precession, the first tables of the motion of the Sun and Moon, a star catalog of 850 stars (Hipparachus, (2nd century BC);
  • the idea of ​​the movement of the Earth around the Sun and determining the size of the Earth (Aristarchus of Samos, Eratosthenes 3-2 centuries BC);
  • the introduction of the Julian calendar into the Roman Empire (46 BC);
  • Claudius Ptolemy - "Syntax" (Almogest) - encyclopedia of ancient astronomy, theory of motion, planetary tables (140 AD).

The poems of Homer and Hesiod give an idea of ​​the astronomical knowledge of the Greeks of this period: a number of stars and constellations are mentioned there, practical advice is given on the use of celestial bodies for navigation and for determining the seasons of the year. The cosmological ideas of this period were entirely borrowed from myths: the Earth is considered flat, and the sky is a solid bowl based on the Earth. The main characters of this period are philosophers, intuitively groping for what will later be called the scientific method of cognition. At the same time, the first specialized astronomical observations are being made, the theory and practice of the calendar is being developed; for the first time, geometry is taken as the basis of astronomy, a number of abstract concepts of mathematical astronomy are introduced; attempts are being made to find physical patterns in the movement of the luminaries. A number of astronomical phenomena were scientifically explained, the sphericity of the Earth was proved.

II Pre-telescopic period. (our era before 1610). The decline of science and astronomy. The collapse of the Roman Empire, the raids of the barbarians, the birth of Christianity. The rapid development of Arabic science. The revival of science in Europe. Modern heliocentric system of world structure.

Claudius Ptolemy (Claudius Ptolomeus)(87-165, Dr. Rome), BIROUNI, Abu Reyhan Mohammed ibn Ahmed al-Biruni(973-1048, modern Uzbekistan), Mirza Mohammed ibn Shahrukh ibn Timur (Taragai) ULUGBEK(1394 -1449, modern Uzbekistan), Nicolaus COPERNICK(1473-1543, Poland), Tycho (Tige) BRAGE(1546-1601, Denmark).

• Arabic period. After the fall of the ancient states in Europe, ancient scientific traditions (including astronomy) continued to develop in the Arab caliphate, as well as in India and China.
  • 813 Establishment of an astronomical school (house of wisdom) in Baghdad;
  • 827 determination of the size of the globe by degree measurements between the Tigris and the Euphrates;
  • 829 foundation of the Baghdad Observatory;
  • 10th century the discovery of the lunar inequality (Abu-l-Wafa, Baghdad);
  • catalog of 1029 stars, clarification of the inclination of the ecliptic to the equator, determination of the length of 1° meridian (1031g, Al-Biruni);
  • numerous works on astronomy until the end of the 15th century (calendar of Omar Khayyam, "Ilkhan tables" of the movement of the Sun and planets (Nasiraddin Tussi, Azerbaijan), works of Ulugbek);
• European revival. At the end of the 15th century, a revival of astronomical knowledge began in Europe, which led to the first revolution in astronomy. This revolution in astronomy was caused by the requirements of practice - the era of great geographical discoveries began.
  • Long-distance voyages required precise methods for determining coordinates. The Ptolemaic system could not meet the increased needs. The countries that were the first to pay attention to the development of astronomical research achieved the greatest success in discovering and developing new lands.
  • In Portugal, back in the 14th century, Prince Henry founded an observatory to meet the needs of navigation, and Portugal was the first European country to begin capturing and exploiting new territories.
  • The most important achievements of European astronomy of the XV-XVI centuries are planetary tables (Regiomontanus from Nuremberg, 1474),
  • the works of N. Copernicus, who made the first revolution in Astronomy (1515-1540),
  • observations by the Danish astronomer Tycho Brahe at the Uraniborg observatory on the island of Van (the most accurate in the pre-telescopic era).

III Telescopic before the advent of spectroscopy (1610-1814). The invention of the telescope and observation with it. The laws of planetary motion. Discovery of the planet Uranus. The first theories of the formation of the solar system.

Scientists who made a significant contribution to the development of astronomy in this period: Galileo Galilei(1564-1642, Italy), Johannes KEPLER(1571-1630, Germany), Jan GAVEL (GAVELIUS) (1611-1687, Poland), Hans Christian HUYGENS(1629-1695, Netherlands), Giovanni Domenico (Jean Dominic) CASINI>(1625-1712, Italy-France), Isaac Newton(1643-1727, England), Edmund GALLEY (HALLEY, 1656-1742, England), William (William) Wilhelm Friedrich HERSHEL(1738-1822, England), Pierre Simon Laplace(1749-1827, France).

• At the beginning of the 17th century (Lippershey, Galileo, 1608) an optical telescope was created, which greatly expanded the horizon of mankind's knowledge of the world.
  • the parallax of the Sun is determined (1671), which made it possible to determine the astronomical unit with high accuracy and determine the speed of light,
  • the subtle movements of the Earth's axis, the proper movements of the stars, the laws of the motion of the Moon,
  • in 1609-1618 Kepler, based on these observations of the planet Mars, discovered three laws of planetary motion,
  • in 1687 Newton published the law of universal gravitation, which explains the causes of the motion of the planets.
  • celestial mechanics is created;
  • the masses of the planets are determined;
  • at the beginning of the 19th century (January 1, 1801), Piazzi discovers the first minor planet (asteroid) Ceres;
  • Pallas and Juno were discovered in 1802 and 1804.

IV Spectroscopy and photography. (1814-1900). Spectroscopic observations. The first determination of the distance to the stars. Discovery of the planet Neptune.

Scientists who made a significant contribution to the development of astronomy in this period: Joseph von Fraunhofer(1787-1826, Germany), Vasily Yakovlevich (Friedrich Wilhelm Georg) STRUVE(1793-1864, Germany-Russia), George Biddell ERI(AIRIE, 1801-1892, England), Friedrich Wilhelm BESSEL(1784-1846, Germany), Johann Gottfried HALLE(1812-1910, Germany), William HEGGINS (Huggins, 1824-1910, England), Angelo SECCHI(1818-1878, Italy), Fedor Alexandrovich BREDIKHIN(1831-1904, Russia), Edward Charles Pickering(1846-1919, USA).

• In 1806 - 1817, I. Fraunthofer (Germany) created the foundations of spectral analysis, measured the wavelengths of the solar spectrum and absorption lines, thus laying the foundations of astrophysics.
• In 1845, I. Fizeau and J. Foucault (France) obtained the first photographs of the Sun.
• In 1845 - 1850, Lord Ross (Ireland) discovered the spiral structure of some nebulae.
• in 1846, I. Galle (Germany), according to the calculations of W. Le Verrier (France), discovered the planet Neptune, which was a triumph of celestial mechanics
• The introduction of photography into astronomy made it possible to obtain photographs of the solar corona and the surface of the Moon, and to begin studying the spectra of stars, nebulae, and planets.
• Progress in optics and telescope construction made it possible to discover the satellites of Mars, to describe the surface of Mars by observing it in opposition (D. Schiaparelli)
• Increasing the accuracy of astrometric observations made it possible to measure the annual parallax of stars (Struve, Bessel, 1838), and to discover the movement of the earth's poles.

V-th Modern period (1900-present). Development of the application of photography and spectroscopic observations in astronomy. Solving the problem of the energy source of stars. Discovery of galaxies. The emergence and development of radio astronomy. Space research.

• At the beginning of the 20th century, K.E. Tsiolkovsky published the first scientific essay on astronautics - “The study of world spaces with jet devices”.
• In 1905 A. Einstein creates the special theory of relativity
• in 1907 - 1916, the general theory of relativity, which made it possible to explain the existing contradictions between the existing physical theory and practice, gave impetus to unravel the mystery of the energy of stars, stimulated the development of cosmological theories
• In 1923, E. Hubble proved the existence of other star systems - galaxies
• in 1929, E. Hubble discovered the law of "red shift" in the spectra of galaxies.
• in 1918, a 2.5-meter reflector was installed at the Mount Wilson Observatory, and in 1947 a 5-meter reflector was put into operation there)
• Radio astronomy emerged in the 1930s with the advent of the first radio telescopes.
• In 1933 Karl Jansky of Bell Labs discovered radio waves coming from the center of the galaxy.
• Grote Reber built the first parabolic radio telescope in 1937.
• In 1948, rocket launches into the high layers of the atmosphere (USA) made it possible to detect X-ray radiation from the solar corona.
• Aronomists began to study the physical nature of celestial bodies and significantly expanded the boundaries of the space under study.
• Astrophysics has become the leading branch of astronomy; it has received especially great development in the 20th century. and continues to grow rapidly today.
• In 1957, the foundation was laid for qualitatively new research methods based on the use of artificial celestial bodies, which subsequently led to the emergence of new branches of astrophysics.
• In 1957, the USSR launched the first artificial Earth satellite, which marked the beginning of the space age for mankind.
• Spacecraft made it possible to bring infrared, X-ray and gamma-ray telescopes out of the earth's atmosphere).
• The first manned space flights (1961, USSR), the first landing of people on the moon (1969, USA) are epoch-making events for all mankind.
• Delivery of lunar soil to Earth (Luna-16, USSR, 1970),
• Landing of descent vehicles on the surface of Venus and Mars,
• Sending automatic interplanetary stations to the more distant planets of the solar system.

(For more details see Timeline of space exploration and Timeline of space exploration.)

1.1.2 Connection of astronomy with other sciences.

Growing out of a once single science of nature - philosophy - astronomy, mathematics and physics have never lost a close connection with each other. Astronomy has played such a leading role in the history of science that many scientists have taken tasks from it and created methods for solving these problems. Astronomy, mathematics and physics have never lost their relationship, which is reflected in the activities of many scientists.

The connection of astronomy with other sciences- Interpenetration and mutual influence of scientific fields:

1.1.3 Structure and scale of the Universe

You already know that our Earth with its satellite Moon, other planets and their satellites, comets and minor planets revolve around the Sun, that all these bodies make up solar system. In turn, the Sun and all other stars visible in the sky are part of a huge star system - ours. Galaxy. The closest star to the solar system is so far away that light, which travels at a speed of 300,000 km/s, travels from it to Earth for more than four years. Stars are the most common type of celestial bodies, with hundreds of billions of them in our galaxy alone. The volume occupied by this star system is so large that light can only cross it in 100,000 years.

In Universe There are many other galaxies like ours. It is the location and movement of galaxies that determines the structure and structure of the universe as a whole. The galaxies are so far apart that with the naked eye you can see only the next three: two in the Southern Hemisphere, and from the territory of Russia only one - the Andromeda Nebula. From the most distant galaxies, light reaches the Earth in 10 billion years. A significant part of the matter of stars and galaxies is in such conditions that it is impossible to create in terrestrial laboratories. All outer space is filled with electromagnetic radiation, gravitational and magnetic fields, between stars in galaxies and between galaxies there is a very rarefied substance in the form of gas, dust, individual molecules, atoms and ions, atomic nuclei and elementary particles.

All bodies in the Universe form systems of varying complexity:

1. solar system - The Sun and celestial bodies moving around it (planets, comets, satellites of planets, asteroids), the Sun is a self-luminous body, other bodies, like the Earth, shine with reflected light. The age of the SS is ~5 billion years. There are a huge number of such star systems with planets and other bodies in the Universe.
2. Stars visible in the sky , including Milky Way is a tiny fraction of the stars that make up galaxies (or call our galaxy the Milky Way) - systems of stars, their clusters and the interstellar medium. There are many such galaxies, the light from the nearest ones travels to us for millions of years. The age of the Galaxies is 10-15 billion years.
3. galaxies unite in a kind of clusters (systems)

All bodies are in constant motion, change, development. Planets, stars, galaxies have their own history, often counted in billions of years.

As you know, the distance to the closest celestial body to the Earth - the Moon is approximately 400,000 km. The most distant objects are located from us at a distance that exceeds the distance to the moon by more than 10 times.

Let's try to imagine the sizes of celestial bodies and the distances between them in the Universe, using a well-known model - the school globe of the Earth, which is 50 million times smaller than our planet. In this case, we must depict the Moon as a ball with a diameter of 7 cm, located at a distance of about 7.5 m from the globe. The model of the Sun will have a diameter of 28 m and be at a distance of 3 km, and the model of Pluto - the most distant planet in the solar system - will be removed from us for 120 km. The nearest star to us at this scale of the model will be located at a distance of about 800,000 km, i.e., 2 times farther than the Moon. Our galaxy will shrink to about the size of the solar system, but the most distant stars will still be outside it.

The diagram shows the system and distances:

1 astronomical unit = 149.6 million km(mean distance from the Earth to the Sun).

1pc (parsec) = 206265 AU = 3, 26 St. years

1 light year(St. year) is the distance that a beam of light travels at a speed of almost 300,000 km / s in 1 year. 1 light year is equal to 9.46 million million kilometers!

1.1.4 Features of astronomy and its methods

For thousands of years, astronomers have studied the position of celestial objects in the starry sky and their mutual movement over time. That is why, for a long time, or rather from the III century BC, dominated geocentric system of the world order of Claudius Ptolemy. Recall that according to it, the planet Earth was at the center of the entire universe, and all other celestial bodies, including the Sun, revolved around it.

And only in the middle of the 16th century, or rather in 1543, did the great work of Nicolaus Copernicus “On the Revolution of the Celestial Spheres” come out, in which he argued that the center of our system is not the Earth, but the Sun. That's how it came about heliocentric doctrine, which gave the key to the knowledge of the universe.

Astronomical observations serve as the main method of studying celestial objects and phenomena.

Astronomical observations are purposeful and active registration of information about the processes and phenomena occurring in the Universe.

Astronomy studies the structure of the Universe, movement, physical nature, origin and evolution of celestial bodies and the systems formed by them. Astronomy also explores the fundamental properties of the universe around us. Huge spatio-temporal scales of the studied objects and phenomena determine distinctive features of astronomy.

Information about what is happening outside the Earth in outer space, scientists receive mainly on the basis of the light and other types of radiation coming from these objects. Observations are the main source of information in astronomy. This first feature astronomy distinguishes it from other natural sciences (for example, physics or chemistry), where experiments play a significant role. Opportunities for experiments outside the Earth appeared only thanks to astronautics. But even in these cases, we are talking about conducting experimental studies on a small scale, such as, for example, studying the chemical composition of lunar or Martian rocks. It is difficult to imagine experiments on a planet as a whole, a star or a galaxy.

Second feature due to the significant duration of a number of phenomena studied in astronomy (from hundreds to millions and billions of years). Therefore, it is impossible to directly observe the changes taking place. Even the changes that occur on the Sun are recorded on Earth only after 8 minutes and 19 seconds (this is how much time it takes for light to travel the distance from the Sun to the Earth). As for distant galaxies, here we are already talking about billions of years. That is, by studying distant star systems, we are studying their past. When the changes are especially slow, one has to observe many related objects, such as stars. Basic information about the evolution of stars is obtained in this way.

Third feature astronomy is due to the need to indicate the position of celestial bodies in space (their coordinates) and the inability to distinguish which of them is closer and which is farther from us. At first glance, all the observed luminaries seem equally distant to us. It seems to us, as to people in antiquity, that all the stars are equally distant from us and are located on a certain spherical surface of the sky - the celestial sphere - which, as a whole, revolves around the Earth.

So, as a science, astronomy is based primarily on observations. Unlike physicists, astronomers are deprived of the opportunity to experiment. Almost all information about celestial bodies is brought to us by electromagnetic radiation. Only in the last forty years have individual worlds been studied directly: to probe the atmospheres of planets, to study the lunar and Martian soil, to study directly the atmosphere of Titan.

In the 19th century, physical research methods penetrated into astronomy, and a symbiotic science arose - astrophysics, which studies the physical properties of cosmic bodies. Astrophysics divided into: a) practical astrophysics, which develops and applies practical methods of astrophysical research and related tools and instruments that can obtain the most complete and objective information about cosmic bodies; b) theoretical astrophysics, in which, on the basis of the laws of physics, explanations are given for the observed physical phenomena.

Modern astronomy – fundamental physical and mathematical science, the development of which is directly related to scientific and technological progress (STP). To study and explain processes, the entire modern arsenal of various, newly emerged sections of mathematics and physics is used. There is also astronomer's profession. Astronomers in our country are trained in the physics or physics and mathematics faculties of Moscow, St. Petersburg, Kazan, Yekaterinburg and some other universities. About 100 specialists are trained per year. About 2,000 astronomers worked on the territory of the former USSR (now in Russia there are about 1,000, and about 100 are actively working), and there are about 10,000 professional astronomers in the world. A real astronomer is a person of broad outlook. To work as an astronomer, one must know physics, chemistry, biology, not to mention the obligatory mathematics. Russian scientists made the most important fundamental discoveries in astronomy. Georgy Gamow predicted the expansion of the universe. Alexander Friedman created the theory of a non-stationary universe, although Einstein argued that it was stationary. Zel'dovich foresaw accretion, that is, the fallout of matter into black holes. Shklovsky predicted the radio lines of neutral hydrogen. Synchrotron radiation was described by Ginzburg. But the experimental verification of these theoretical works was carried out by the Americans, for which they received Nobel Prizes. We have never had such equipment, such telescopes as in the USA.

The main habitats of astronomers:

• State Institute. P.K. Sternberg (GAISH MSU)
• Space Research Institute
• Institute of Astronomy and Physical Institute of the Russian Academy of Sciences
• Main (Pulkovo) Astronomical Observatory
• Special Astrophysical Observatory of the Russian Academy of Sciences (Northern Caucasus)

The main sections of astronomy:

1.1.5 Telescopes

For research to be accurate, special tools and devices are needed.

one). It is established that Thales of Miletus in 595 BC first used gnomon(an ancient astronomical instrument, a vertical object (an obelisk rod, a column, a pole), which makes it possible to determine the angular height of the Sun by the shortest length of its shadow (at noon). This made it possible to use this instrument as a sundial, and to determine the stages of the solstice, equinox, the length of the year , latitude of the observer and much more.

2). Hipparchus (180-125 AD, Ancient Greece) used an astrolabe, which allowed him to measure the parallax of the Moon, in 129 BC, set the length of the year at 365.25 days, determine the procession and compile in 130 BC. star catalog for 1008 stars, etc.

At various times, there were both an astronomical staff and an astrolabon (this is the first type of theodolite), a quadrant and many other devices and instruments. Observations of celestial bodies and objects are carried out in special institutions - observatories, which arose at the very beginning of the development of astronomy BC. e.

Astronomical observatories were created for possible research and observations in different countries. In our country, there are about two dozen of them: the Main Pulkovo Astronomical Observatory of the Russian Academy of Sciences (GAO RAS), the State Astronomical Institute. P.K. Sternberg (GAISh), Caucasian Mountain Observatory (KGO SAISH), etc.

Real astronomical research began when, in 1609, they invented telescope.

A revolution in astronomy occurred in 1608, after Dutch spectacle maker John Lippershey discovered that two lenses placed in a straight line could magnify objects. Thus the spotting scope was invented.

This idea was immediately taken advantage of by Galileo. In 1609, he built his first 3x telescope and pointed it into the sky. So the telescope turned into a telescope.

The telescope has become the main instrument used in astronomy to observe celestial bodies, receive and analyze the radiation coming from them. . This word comes from two Greek words: tele - far and skopeo - I look.

Telescope - an optical instrument that increases the angle of view at which celestial bodies are visible ( resolution), and collects many times more light than the observer's eye ( penetrating power).

The telescope is used, firstly, in order to collect as much light as possible coming from the object under study, and secondly, to provide an opportunity to study its small details that are inaccessible to the naked eye. The fainter objects the telescope makes it possible to see, the more penetrating power. The ability to distinguish fine details characterizes resolution telescope. Both of these characteristics of a telescope depend on the diameter of its objective.

The amount of light collected by the lens increases in proportion to its area (the square of the diameter). The pupil diameter of the human eye, even in complete darkness, does not exceed 8 mm. The lens of a telescope can exceed the diameter of the pupil of the eye by tens and hundreds of times. This allows the telescope to detect stars and other objects that are 100 million times fainter than objects visible to the naked eye.

How the telescope works:

Parallel rays of light (for example, from a star) fall on the lens. The lens builds an image in the focal plane. Rays of light parallel to the main optical axis are collected at the focus F, which lies on this axis. Other beams of light are collected near the focus - above or below. This image is viewed by an observer using an eyepiece.

As you know, if the object is farther than twice the focal length, it gives a reduced, inverted and real image of it. This image is located between the focus and dual focus points of the lens. The distances to the Moon, planets, and even more stars are so great that the rays coming from them can be considered parallel. Hence, the image of the object will be located in the focal plane.

The diameters of the input and output beams are very different (the input has the diameter of the objective, and the output has the diameter of the image of the objective built by the eyepiece). In a properly adjusted telescope, all the light collected by the lens enters the observer's pupil. In this case, the gain is proportional to the square of the ratio of the lens and pupil diameters. For large telescopes, this value is tens of thousands of times. This is how one of the main tasks of the telescope is solved - to collect more light from the observed objects. If we are talking about a photographic telescope - an astrograph, then the illumination of the photographic plate increases in it.

Main characteristics of telescopes.

1) Telescope aperture(D)- is the diameter of the main mirror of the telescope or its converging lens.

The more aperture, the more light the lens will collect and the fainter objects you will see.

2) F focal length of the telescope - This is the distance at which a mirror or objective lens constructs an image of an infinitely distant object.

Usually this refers to the focal length of the lens (F), since the eyepieces are interchangeable, and each of them has its own focal length.

From focal length depends not only on the magnification, but also on the quality of the image. The more focal length, the better the image quality. The length of a telescope, especially Newton's reflectors and refractors, also depends on the focal length of the telescope.

3) Magnification (or magnification) of the telescope(W) shows how many times the telescope can magnify an object orthe angle at which an observer sees an object. It is equal to the ratio of the focal lengths of the objective F and the eyepiece f.

The telescope increases the visible angular dimensions of the Sun, the Moon, the planets and details on them, but the stars, due to their colossal distance, are still visible through the telescope as luminous dots.

F you most often cannot change, but having eyepieces with different f, you can change magnification or magnification of the telescope D. Having interchangeable eyepieces, it is possible to obtain different magnifications with the same lens. So the capabilities of a telescope in astronomy are usually characterized not by the increase, but by the diameter of its lens. In astronomy, as a rule, magnifications of less than 500 times are used. The use of large magnifications is hindered by the Earth's atmosphere. The movement of air, imperceptible to the naked eye (or at low magnifications), leads to the fact that small details of the image become blurry, blurred. Astronomical observatories, which use large telescopes with a mirror diameter of 2–3 m, try to locate in areas with a good astroclimate: a large number of clear days and nights, with high atmospheric transparency.

4) Resolution – minimum angle between two stars seen separately. Simply put, resolution can be understood as the "clarity" of an image.

Resolution can be calculated using the formula:

where δ is the angular resolution in seconds, D

The distance between objects in the sky in astronomy is measured angle, which is formed by rays drawn from the point at which the observer is located to objects. This distance is called corner, and expressed in degrees and fractions of a degree:

degrees - 5 o, minutes - 13 "seconds - 21"

The human eye, without special instruments, distinguishes 2 stars separately from each other if their angular distance is at least 1-2 ". The telescope allows you to reduce this limit by several times. In the largest telescopes, you can see separate stars, the angular distances of which can be hundredths and thousandths shares.

The angle at which we see the diameter of the Sun and the Moon ~ 0.5 o = 30".

The limitation on the maximum magnification is imposed by the phenomenon of diffraction - the bending of light waves around the edges of the lens. Due to diffraction, instead of the image of a point, rings are obtained. The angular size of the central spot ( theoretical angular resolution):

where δ is the angular resolution in seconds, λ - radiation wavelength , D is the lens diameter in millimeters.

The smaller the size of the image of a luminous point (star) that a telescope lens gives, the better its resolution. If the distance between the images of two stars is less than the size of the image itself, then they merge into one. The minimum size of a star image (in arcseconds) can be calculated using the formula:

Where λ is the wavelength of light, a D is the lens diameter. A school telescope with a 60 mm objective lens would have a theoretical resolution of about 2 Ѕ . Recall that this exceeds the resolution of the naked eye (2") by 60 times. The actual resolution of the telescope will be less, since the quality of the image is significantly affected by the state of the atmosphere, air movement.

For visible wavelengths at λ = 550 nm on a telescope with a diameter D= 1 m, the theoretical angular resolution will be δ = 0.1". In practice, the angular resolution of large telescopes is limited by atmospheric tremor. In photographic observations, the resolution is always limited by the Earth's atmosphere and guiding errors and cannot be better than 0.3". When observing with the eye, due to the fact that one can try to catch the moment when the atmosphere is relatively calm (a few seconds are enough), the resolution of telescopes with a diameter D, large 2 m, may be close to theoretical. A telescope is considered good if it collects more than 50% of the radiation in a 0.5" circle.

Ways to increase the resolution of the telescope:

1) increasing the diameter of the telescope

2) decrease in the wavelength of the studied radiation

5) Penetrating power telescopea characterized by the limiting magnitude m of the faintest star that can be seen with this instrument under the best observing conditions. For such conditions, the penetrating force can be determined by the formula:

m= 2.1 + 5 lg D

where D is the lens diameter in millimeters, m is the limiting magnitude.

6) Relative hole – diameter ratioDto focal length F:

Telescopes for visual observations typically have aperture ratios of 1/10 or less. For modern telescopes, it is 1/4 or more.

7) Often, instead of a relative hole, the concept is used luminosity equal to ( D/F) 2 . Aperture characterizes the illumination created by the lens in the focal plane.

8) Relative focal length of the telescope(denoted by the inverted letter A) is the reciprocal of the relative hole:

In photography, this quantity is often called diaphragm .

Relative aperture and relative focal length are important characteristics of a telescope objective. These are the opposite of each other. The larger the relative aperture, the smaller the relative focal length and the greater the illumination in the focal plane of the telescope lens, which is beneficial for photography (allows you to reduce shutter speed while maintaining exposure). But at the same time, a smaller image scale is obtained on the photodetector frame.

Let's build the image of the Moon, which gives the lens with focal length F(Fig. 1.6). It can be seen from the figure that the lens does not change the angular dimensions of the observed object - the angle α. Let us now use one more lens - eyepiece 2, placing it from the image of the Moon (point F1) at a distance equal to the focal length of this lens - f, exactly F2. The focal length of the eyepiece must be less than the focal length of the objective. Having built the image that the eyepiece gives, we will make sure that it increases the angular dimensions of the Moon: the angle β is noticeably larger than the angle α.

Types of telescopes:

1. Optical telescopes
   1. Refractor.
   2. Reflector.
   3. Mirror lens.

If a lens is used as the objective of a telescope, then it is called refractor(from the Latin word refracto - I refract), and if a concave mirror, then reflector(reflecto - I reflect). Mirror-lens telescopes use a combination of a mirror and lenses.

Telescope - refractor uses light refraction. The rays that come from the heavenly bodies are collected by a lens or lens system.

The main part of the protozoan refractor – lens - a biconvex lens mounted in front of the telescope. The lens collects radiation. The larger the lens D, the more radiation the telescope collects, the weaker sources can be detected by it. To avoid chromatic aberration, lenses are made composite. However, in cases where it is required to minimize scattering in the system, a single lens must also be used. The distance from the lens to the main focus is called main focal length F.

Telescope - reflector uses light reflection. They use a concave mirror capable of focusing reflected rays.

main element reflector is a mirror - a reflective surface of a spherical, parabolic or hyperbolic shape. It is usually made from a round piece of glass or quartz and then coated with a reflective coating (a thin layer of silver or aluminum). The manufacturing accuracy of the mirror surface, i.e. the maximum allowable deviations from a given shape depends on the wavelength of light at which the mirror will operate. Accuracy should be better than λ/8. For example, a mirror operating in visible light (wavelength λ = 0.5 microns) must be manufactured with an accuracy of 0.06 microns (0.00006 mm).

The optical system facing the observer's eye is called eyepiece . In the simplest case, the eyepiece can consist of only one positive lens (in this case, we will get an image highly distorted by chromatic aberration).

In addition to refractors and reflectors, various types are currently in use. mirror-lens telescopes.

School telescopes are mostly refractors, usually with a biconvex converging lens as their objective.

In the current observatories we can see large optical telescopes. The largest reflecting telescope in Russia, which has a mirror with a diameter of 6 m, was designed and built by the Leningrad Optical and Mechanical Association. It is called the "Large Azimuth Telescope" (abbreviated as BTA).

Its huge concave mirror, which has a mass of about 40 tons, is ground to within fractions of a micrometer. The focal length of the mirror is 24 m. The mass of the entire telescope installation is more than 850 tons, and the height is 42 m. The telescope is controlled by a computer, which allows you to accurately point the telescope at the object under study and keep it in the field of view for a long time, smoothly turning the telescope following the rotation of the Earth . The telescope is part of the Special Astrophysical Observatory of the Russian Academy of Sciences and is installed in the North Caucasus (near the village of Zelenchukskaya in the Karachay-Cherkess Republic) at an altitude of 2100 m above sea level.

At present, it has become possible to use in ground-based telescopes not monolithic mirrors, but mirrors consisting of separate fragments. Two telescopes have already been built and are operating, each of which has a lens diameter 10 m, consisting of 36 separate hexagonal mirrors. By controlling these mirrors with a computer, you can always arrange them so that they all collect light from the observed object in a single focus. It is planned to create a telescope with a composite mirror with a diameter of 32 m, operating on the same principle.

Telescopes are very different - optical (general astrophysical purpose, coronographs, telescopes for observing satellites), radio telescopes, infrared, neutrino, x-ray. For all their diversity, all telescopes that receive electromagnetic radiation decide two main tasks:

• create the sharpest possible image and, in case of visual observations, increase the angular distances between objects (stars, galaxies, etc.);
• collect as much radiation energy as possible, increase the illumination of the image of objects.

Modern telescopes are often used to photograph the image that a lens gives. This is how those photographs of the Sun, galaxies and other objects that you will see on the pages of the textbook, in popular books and magazines, and on sites on the Internet were obtained. Telescopes adapted for photographing celestial objects are called astrographs. Photographic observations have a number of advantages over visual ones. The main benefits include:

1. documentation - the ability to record the occurring phenomena and processes, and for a long time to save the information received;
2. immediacy - the ability to register short-term phenomena occurring at the moment;
3. panorama - the ability to capture several objects on a photographic plate at the same time and their relative position;
4. integrality - the ability to accumulate light from weak sources; the detail of the resulting image.

With the help of telescopes, not only visual and photographic observations are made, but mainly high-frequency photoelectric and spectral observations. Information about the temperature, chemical composition, magnetic fields of celestial bodies, as well as their movement is obtained from spectral observations. In addition to light, celestial bodies emit electromagnetic waves that are longer than light (infrared, radio waves) or shorter than light (UV, X-rays, and gamma rays).

The study of the Universe began and continues for several millennia, but until the middle of the last century, research was exclusively in optical range electromagnetic waves. Therefore, the available radiation region was the range from 400 to 700 nm. The first astronomical scientific observations were astrometric, only the location of the planets, stars and their apparent movement in the celestial sphere were studied.

But celestial bodies give different radiation: visible light, infrared, ultraviolet, radio waves, x-rays, gamma radiation. In the 20th century, astronomy became all-wave. Astronomy is called all-wave, since observations of objects are carried out not only in the optical range. Currently, radiation from space objects is recorded in the entire range of the electromagnetic spectrum from long-wave radio emission (frequency 10 7 , wavelength l = 30 m) to gamma radiation (frequency 10 27 Hz, wavelength l = 3∙10 –19 ×m = 3∙10 –10 nm). For this purpose, various devices are used, each of which is capable of receiving radiation in a certain range of electromagnetic waves: infrared, ultraviolet, x-ray, gamma and radio radiation.

To receive and analyze optical and other types of radiation in modern astronomy, the entire arsenal of achievements in physics and technology is used - photomultipliers, electron-optical converters, etc. At present, the most sensitive light receivers are charge-coupled devices (CCDs), which allow recording individual light quanta . They are a complex system of semiconductors (semiconductor arrays) that use an internal photoelectric effect. In this and other cases, the data obtained can be reproduced on a computer display or presented for processing and analysis in digital form.

Observations in other spectral ranges made it possible to make important discoveries. First invented radio telescopes. Radio emission from space reaches the Earth's surface without significant absorption. To receive it, the largest astronomical instruments, radio telescopes, were built.

Their metal antenna mirrors, which reach a diameter of several tens of meters, reflect radio waves and collect them like an optical reflecting telescope. To register radio emission, special sensitive radio receivers are used. Any radio telescope it is similar to optical in principle of operation: it collects radiation and focuses it on a detector tuned to a selected wavelength, and then converts this signal, showing a conventionally colored image of the sky or object.

So, radio waves brought information about the presence of large molecules in cold molecular clouds, about active galaxies, about the structure of the nuclei of galaxies, including our Galaxy, while optical radiation from the center of the Galaxy is completely delayed by cosmic dust.

To significantly improve the angular resolution, radio astronomy uses radio interferometers. The simplest radio interferometer consists of two radio telescopes separated by a distance called interferometer base. Radio telescopes located in different countries and even on different continents can also be connected into a single observing system. Such systems are called ultra-long baseline radio interferometers(RSDB). Such systems provide the highest possible angular resolution, several thousand times better than any optical telescope.

Our Earth is reliably protected by the atmosphere from penetrating hard electromagnetic radiation, from infrared radiation. Since the atmosphere prevents the penetration of rays to the earth c λ< λ света (ультрафиолетовые, рентгеновские, γ - излучения), то последнее время на орбиту Земли выводятся телескопы и целые орбитальные обсерватории: (т.е развиваются внеатмосферные наблюдения). Т.е. современные инфракрасные, рентгеновские и гамма обсерватории вынесены за пределы земной атмосферы.

Instruments for studying other types of radiation are also usually called telescopes, although in their design they sometimes differ significantly from optical telescopes. As a rule, they are installed on artificial satellites, orbital stations and other spacecraft, since these radiations practically do not penetrate through the earth's atmosphere. She disperses and absorbs them.

Even optical telescopes in orbit have certain advantages over those on the ground. Most big of them space telescope. Hubble created in the USA with mirror diameter 2.4 m objects are available that are 10–15 times fainter than the same telescope on Earth. Its resolution is 0.1S, which is unattainable even for larger ground-based telescopes. Images of nebulae and other distant objects show fine details that are indistinguishable when observed from Earth.

1.1.6 Let's consider telescopes by their types in more detail.

1) Refractor(refracto - I refract) - the refraction of light in the lens is used (refractive).

The first telescope was a refractor telescope with a single lens as an objective. "Spotting scope" made in Holland [H. Lippershey]. According to a rough description, Galileo Galilei made it in 1609 and first sent it to the sky in November 1609, and in January 1610 discovered 4 satellites of Jupiter.

Nowadays, refractors with a single lens are used, perhaps, only in coronographs and some spectral instruments. All modern refractors are equipped with achromatic objectives. The largest refractor in the world is the telescope of the Yerk Observatory (USA) with a 1m lens. Manufactured by Alvan Clark (US Optician). Its lens is 102 cm (40 inches) and was installed in 1897 at the Yerk Observatory (near Chicago). It was built at the end of the last century, and since then, professionals have not built giant refractors. Clark made another 30 inch refractor, which was installed in 1885 at the Pulkovo Observatory and destroyed during the Second World War.

40-inch refractor telescope at the Yerkes Observatory. Snapshot 2006 (Wikipedia)

b) Reflector(reflecto - reflect) - a concave mirror is used to focus the rays.

Newton reflector.

In 1667, the first mirror telescope was invented by I. Newton (1643-1727, England) with a mirror diameter of 2.5 cm at 41 x magnification. Here, a flat diagonal mirror located near the focus deflects the beam of light outside the tube, where the image is viewed through the eyepiece or photographed. The main mirror is parabolic, but if the aperture ratio is not too large, it can be spherical. In those days, mirrors were made from metal alloys and quickly dimmed.

The largest telescope in the world W. Keka installed in 1996 a mirror diameter of 10 m (the first of two, but the mirror is not monolithic, but consists of 36 hexagonal mirrors) at the Maun Kea Observatory (California, USA).

Keck Observatory

Segmented primary mirror of the Keck II telescope

In 1995, the first of four telescopes (mirror diameter 8m) was put into operation (ESO observatory, Chile).

Prior to this, the largest was in the USSR, the mirror diameter was 6m, installed in the Stavropol Territory (Mount Pastukhov, h = 2070m) at the Special Astrophysical Observatory of the USSR Academy of Sciences (monolithic mirror 42t, 600t telescope, you can see stars 24 m). The Special Astrophysical Observatory of the USSR Academy of Sciences was founded in 1966, 6 years after the decision of the Government to establish the country's largest observatory for fundamental space research. The observatory was created as a center for collective use to ensure the operation of the BTA (Large Azimuthal Telescope) optical telescope with a mirror diameter of 6 meters and the RATAN-600 radio telescope with a ring antenna diameter of 600 meters, then the world's largest astronomical instruments. They were put into operation in 1975-1977 and are designed to study objects of near and far space using ground-based astronomy methods.

BTA tower

c) Mirror-lens.(Schmidt chamber) - a combination of both types.

Schmidt-Cassegrain telescope. Large aperture, free from coma (coma aberration) and with a large field of view.

The first one was built in 1930. B.V. Schmidt (1879-1935, Estonia) with a lens diameter of 44 cm Estonian optician, employee of the Hamburg Observatory Barnhard Schmidt installed a diaphragm in the center of the curvature of a spherical mirror, immediately eliminating both coma (comatic aberration) and astigmatism. To eliminate spherical aberration, he placed a specially shaped lens in the diaphragm. The result is a photographic camera with the only aberration - the curvature of the field and amazing qualities: the larger the aperture of the camera, the better the images it gives, and the larger the field of view!

In 1946 James Baker installed a convex secondary mirror in the Schmidt chamber and got a flat field. Somewhat later, this system was modified and became one of the most advanced systems: Schmidt-Cassegrain, which on a field with a diameter of 2 degrees gives a diffractive image quality.

Schmidt-Cassegrain telescope

In 1941 D.D. Maksutov(USSR) made a meniscus telescope, which is advantageous with a short tube. Used by amateur astronomers.

Telescope Maksutov-Cassegrain.

In 1941 D. D. Maksutov found that the spherical aberration of a spherical mirror can be compensated for by a meniscus of high curvature. Having found a good distance between the meniscus and the mirror, Maksutov managed to get rid of coma and astigmatism. The curvature of the field, as in the Schmidt camera, can be eliminated by installing a plano-convex lens near the focal plane - the so-called Piazzi-Smith lens. Having aluminized the central part of the meniscus, Maksutov obtained meniscus analogues of the Cassegrain and Gregory telescopes. Meniscus analogues of almost all telescopes of interest to astronomers have been proposed.

Telescope Maksutov - Cassegrain with a diameter of 150 mm

In 1995, for an optical interferometer, the first telescope with an 8-m mirror (out of 4) with a base of 100m was put into operation (ATACAMA desert, Chile; ESO).

In 1996, the first telescope with a diameter of 10 m (out of two with a base of 85 m) named after. W. Keka introduced at the Maun Kea Observatory (California, Hawaii, USA)

2. - Benefits: in any weather and time of day, you can observe objects that are inaccessible to optical ones. They represent a bowl (like a locator).

Radio astronomy developed after the war. The largest radio telescopes now are the fixed RATAN-600, Russia (commissioned in 1967, 40 km from the optical telescope, consists of 895 individual mirrors 2.1x7.4 m in size and has a closed ring with a diameter of 588 m), Arecibo (Puerto Rico, 305 m - concrete bowl of an extinct volcano, introduced in 1963). Of the mobile ones, they have two radio telescopes with a 100 m bowl.

Of particular importance in our space age is given to orbital observatories. The most famous of them is space telescope. Hubble- launched in April 1990 and has a diameter of 2.4 m. After installing the corrective block in 1993, the telescope registers objects up to the 30th magnitude, and its angular magnification is better than 0.1 "(at this angle a pea is visible from a distance several tens of kilometers).

Schematic diagram of the telescope. Hubble

l. Fixing the material.

1. What astronomical information did you study in courses of other subjects? (natural science, physics, history, etc.)
2. What have you learned?
3. What is astronomy? Features of astronomy, etc.
4. What is the specificity of astronomy compared to other natural sciences?
5. What types of celestial bodies do you know?
6. What are the objects of knowledge in astronomy?
7. What methods and tools of knowledge in astronomy do you know?
8. The purpose of the telescope and its types
9. What is the importance of astronomy in the national economy today?

Values ​​in the national economy:

• - Orientation by stars to determine the sides of the horizon
• - Navigation (navigation, aviation, astronautics) - the art of navigating the stars
• - Exploration of the universe to understand the past and predict the future
• - Astronautics:
• - Exploration of the Earth in order to preserve its unique nature
• - Obtaining materials that are impossible to obtain in terrestrial conditions
• - Weather forecast and natural disaster prediction
• - Rescue of ships in distress
• - Exploration of other planets to predict the development of the Earth

1. View the Observer's Calendar, an example of an astronomical journal (electronic, such as the Sky).
2. On the Internet, go to, find lectures on astronomy, see Astrotop astrolinks, portal: Astronomy in Wikipedia, - using which you can get information on the issue of interest or find it.

Followed the movement of the stars in the sky. Astronomical observations of that time helped to navigate the terrain, and were also necessary for the construction of philosophical and religious systems. A lot has changed since then. Astronomy finally freed itself from astrology, accumulated extensive knowledge and technical power. However, astronomical observations made on Earth or in space are still one of the main methods of obtaining data in this science. The methods of collecting information have changed, but the essence of the methodology has remained unchanged.

What are astronomical observations?

There is evidence to suggest that people possessed elementary knowledge about the movement of the Moon and the Sun even in the prehistoric era. The works of Hipparchus and Ptolemy testify that knowledge about the luminaries was also in demand in Antiquity, and much attention was paid to them. For that time and for a long period after, astronomical observations were the study of the night sky and the fixation of what was seen on paper, or, more simply, a sketch.

Until the Renaissance, only the simplest instruments were assistants to scientists in this matter. A significant amount of data became available after the invention of the telescope. As it improved, the accuracy of the information received increased. However, at whatever level of technological progress, astronomical observations are the main way to collect information about celestial objects. Interestingly, this is also one of the areas of scientific activity in which the methods used in the era before scientific progress, that is, observation with the naked eye or with the help of the simplest equipment, have not lost their relevance.

Classification

Today, astronomical observations are a fairly broad category of activities. They can be classified according to several criteria:

• qualifications of the participants;
• the nature of the recorded data;
• location.

In the first case, professional and amateur observations are distinguished. The data obtained in this case is most often the registration of visible light or other electromagnetic radiation, including infrared and ultraviolet. In this case, information can be obtained in some cases only from the surface of our planet or only from space outside the atmosphere: according to the third feature, astronomical observations made on Earth or in space are distinguished.

amateur astronomy

The beauty of the science of the stars and other celestial bodies is that it is one of the few that literally needs active and tireless admirers among non-professionals. A huge number of objects worthy of constant attention, there are a small number of scientists occupied with the most complex issues. Therefore, astronomical observations of the rest of the near space fall on the shoulders of amateurs.

The contribution of people who consider astronomy their hobby to this science is quite tangible. Until the middle of the last decade of the last century, more than half of the comets were discovered by amateurs. Their areas of interest also often include variable stars, observing novae, tracking the coverage of celestial bodies by asteroids. The latter is today the most promising and demanded work. As for the New and Supernovae, as a rule, amateur astronomers are the first to notice them.

Options for non-professional observations

Amateur astronomy can be divided into closely related branches:

• Visual astronomy. This includes astronomical observations with binoculars, a telescope, or the naked eye. The main goal of such activities, as a rule, is to enjoy the opportunity to observe the movement of the stars, as well as from the process itself. An interesting branch of this direction is "sidewalk" astronomy: some amateurs take their telescopes out into the street and invite everyone to admire the stars, planets and the Moon.
• Astrophotography. The purpose of this direction is to obtain photographic images of celestial bodies and their elements.
• Telescope building. Sometimes the necessary optical instruments, telescopes and accessories for them, are made by amateurs almost from scratch. In most cases, however, telescope construction consists in supplementing existing equipment with new components.
• Research. Some amateur astronomers seek, in addition to aesthetic pleasure, to get something more material. They are engaged in the study of asteroids, variables, new and supernovae, comets and meteor showers. Periodically, in the process of constant and painstaking observations, discoveries are made. It is this activity of amateur astronomers that makes the greatest contribution to science.

Activities of professionals

Specialist astronomers around the world have more sophisticated equipment than amateurs. The tasks facing them require high accuracy in collecting information, a well-functioning mathematical apparatus for interpretation and forecasting. As a rule, quite complex, often distant objects and phenomena lie at the center of the work of professionals. Often, the study of the expanses of space makes it possible to shed light on certain laws of the universe, to clarify, supplement or refute theoretical constructions regarding its origin, structure and future.

Classification by type of information

Observations in astronomy, as already mentioned, can be associated with the fixation of various radiation. On this basis, the following directions are distinguished:

• optical astronomy studies radiation in the visible range;
• infrared astronomy;
• ultraviolet astronomy;
• radio astronomy;
• x-ray astronomy;
• gamma astronomy.

In addition, the directions of this science and the corresponding observations that are not related to electromagnetic radiation are highlighted. This includes neutrino, studying neutrino radiation from extraterrestrial sources, gravitational-wave and planetary astronomy.

From the surface

Some of the phenomena studied in astronomy are available for research in ground-based laboratories. Astronomical observations on Earth are associated with the study of trajectories of movement by measuring the distance in space to stars, fixing certain types of radiation and radio waves, and so on. Until the beginning of the era of astronautics, astronomers could only be content with information obtained under the conditions of our planet. And this was enough to build a theory of the origin and development of the Universe, to discover many patterns that exist in space.

High above the earth

With the launch of the first satellite, a new era in astronomy began. The data collected is invaluable. They contributed to the deepening of scientists' understanding of the mysteries of the universe.

Astronomical observations in space make it possible to detect all types of radiation, from visible light to gamma and X-rays. Most of them are not available for research from the Earth, because the atmosphere of the planet absorbs them and does not allow them to the surface. X-ray pulsars are an example of discoveries that became possible only after that.

Information miners

Astronomical observations in space are carried out using various equipment installed on spacecraft and orbiting satellites. Many studies of this nature are carried out on the invaluable contribution of optical telescopes launched several times in the last century. The famous Hubble stands out among them. For the layman, it is primarily a source of stunningly beautiful photographic images of deep space. However, this is not all that he "can do". With its help, a large amount of information about the structure of many objects, the patterns of their "behavior" was obtained. Hubble and other telescopes are an invaluable source of data necessary for theoretical astronomy, working on the problems of the development of the universe.

Astronomical observations - both terrestrial and space - are the only ones for the science of celestial bodies and phenomena. Without them, scientists could only develop various theories without being able to compare them with reality.

Astronomy is a science that studies celestial objects and the Universe in which we live.

Remark 1

Since astronomy as a science does not have the opportunity to conduct an experiment, the main source of information is the information that researchers receive during observation.

In this regard, a field called observational astronomy is singled out in astronomy.

The essence of observational astronomy is to obtain the necessary information about objects in space using instruments such as telescopes and other equipment.

Observations in astronomy make it possible, in particular, to track patterns in the properties of certain objects under study. The obtained results of the study of some objects can be extended to other objects with similar properties.

Sections of observational astronomy

In observational astronomy, the division into sections is associated with the division of the electromagnetic spectrum into ranges.

Optical astronomy - contributes to observations in the visible part of the spectrum. At the same time, mirrors, lenses, and solid-state detectors are used in observation devices.

Remark 2

In this case, the region of visible radiation lies in the middle of the range of the investigated waves. The wavelength of visible radiation is in the range from 400 nm to 700 nm.

Infrared astronomy is based on the search and study of infrared radiation. In this case, the wavelength exceeds the limiting value for observations with silicon detectors: about 1 μm. To study the selected objects in this part of the range, researchers mainly use telescopes - reflectors.

Radio astronomy is based on observations of radiation with a wavelength from millimeters to tens of millimeters. By the principle of their operation, receivers using radio emission are comparable to those receivers that are used in broadcasting radio programs. However, radio receivers are more sensitive.

X-ray astronomy, gamma-ray astronomy and ultraviolet astronomy are included in high energy astronomy.

Observation methods in astronomy

Obtaining the desired data is possible when astronomers register electromagnetic radiation. In addition, researchers conduct observations of neutrinos, cosmic rays or gravitational waves.

Optical and radio astronomy uses ground-based observatories in its activities. The reason for this is that at the wavelengths of these ranges, the atmosphere of our planet has a relative transparency.

Observatories are mostly located at high altitudes. This is due to the reduction in absorption and distortion that the atmosphere creates.

Remark 3

Note that a number of infrared waves are significantly absorbed by water molecules. Because of this, observatories are often built in dry places at high altitude or in space.

Balloons or space observatories are mainly used in the fields of x-ray, gamma-ray and ultraviolet astronomy, and with a few exceptions, in far-IR astronomy. At the same time, observing air showers, you can detect the gamma radiation that created them. Note that the study of cosmic rays is currently a rapidly developing area of ​​astronomical science.

Objects located close to the Sun and to the Earth can be seen and measured when they are observed against the background of other objects. Such observations were used to build models of the orbits of the planets, as well as to determine their relative masses and gravitational perturbations. The result was the discovery of Uranus, Neptune and Pluto.

Radio astronomy - the development of this field of astronomy was the result of the discovery of radio emission. Further development of this area led to the discovery of such a phenomenon as cosmic background radiation.

Neutrino astronomy - this area of ​​astronomical science uses neutrino detectors in its arsenal, located mainly underground. Neutrino astronomy tools help to obtain information about processes that researchers cannot observe with telescopes. An example is the processes occurring in the core of our Sun.

Gravitational wave receivers have the ability to record traces of even such phenomena as the collision of such massive objects as neutron stars and black holes.

Automatic spacecraft are actively used in astronomical observations of the planets of the solar system. The geology and meteorology of the planets are being studied especially actively with their help.

Conditions for conducting astronomical observations.

For better observation of astronomical objects, the following conditions are important:

1. Research is carried out mainly in the visible part of the spectrum using optical telescopes.
2. Observations are mainly carried out at night, since the quality of the data obtained by researchers depends on the transparency of the air and visibility conditions. In turn, the visibility conditions depend on turbulence and the presence of heat flows in the air.
3. The absence of a full moon gives an advantage in observing astronomical objects. If the full moon is in the sky, then this gives additional illumination and complicates the observation of faint objects.
4. For an optical telescope, the most suitable place for observation is open space. In outer space, it is possible to make observations that do not depend on the vagaries of the atmosphere, for lack of such in space. The disadvantage of this method of observation is the high financial cost of such studies.

After space, the most suitable place for observing outer space are the peaks of the mountains. Mountain peaks have a large number of cloudless days and have quality visibility conditions associated with good atmospheric quality.

Example 1

An example of such observatories are the mountain peaks of the islands of Mauna Kea and La Palma.

The level of darkness at night also plays a big role in astronomical observations. Artificial illumination created by human activity interferes with high-quality observation of faint astronomical objects. However, the use of plafonds around street lamps helps to help the problem. As a result, the amount of light reaching the earth's surface increases, and the radiation directed towards the sky decreases.

5. The influence of the atmosphere on the quality of observations can be great. To obtain a better image, telescopes with additional image blur correction are used. To improve the quality, adaptive optics, speckle interferometry, aperture synthesis, or placing telescopes in space are also used.

FOREWORD
The book is devoted to the organization, content and methodology of advanced level astronomical observations, as well as the simplest mathematical methods for their processing. It begins with a chapter on testing the telescope, the main instrument of observational astronomy. This chapter outlines the main issues related to the simplest theory of the telescope. Teachers will find here a lot of valuable practical advice related to determining the various characteristics of a telescope, checking the quality of its optics, choosing the optimal conditions for observing, as well as the necessary information about the most important telescope accessories and how to handle them when making visual and photographic observations.
The most important part of the book is the second chapter, which considers, on the basis of concrete material, questions of the organization, content, and methods of conducting astronomical observations. A significant part of the proposed observations - visual observations of the Moon, Sun, planets, eclipses - does not require high qualifications and, with skillful guidance from the teacher, can be mastered in a short time. At the same time, a number of other observations - photographic observations, visual observations of variable stars, program observations of meteor showers, and some others - already require considerable skill, certain theoretical training and additional instruments and equipment.
Of course, not all of the observations listed in this chapter can be implemented in any school. The organization of observations of increased difficulty is most likely available to those schools where there are good traditions of organizing extracurricular activities in astronomy, there is experience in the relevant work and, which is very important, a good material base.
Finally, in the third chapter, based on specific material, the main mathematical methods for processing observations are presented in a simple and visual form: interpolation and extrapolation, approximate representation of empirical functions, and error theory. This chapter is an integral part of the book. It directs both school teachers and students, and, finally, astronomy lovers to a thoughtful, serious attitude towards setting up and conducting astronomical observations, the results of which can acquire a certain significance and value only after they have been subjected to appropriate mathematical processing.
The attention of teachers is drawn to the need to use microcalculators, and in the future - personal computers.
The material of the book can be used in conducting practical classes in astronomy, provided for by the curriculum, as well as in conducting optional classes and in the work of an astronomical circle.
Taking this opportunity, the authors express their deep gratitude to the Deputy Chairman of the Council of Astronomical Circles of the Moscow Planetarium, an employee of the SAI MSU M. Yu. Shevchenko and Associate Professor of the Vladimir Pedagogical Institute, Candidate of Physical and Mathematical Sciences E. P. Razbitnaya for valuable suggestions that contributed to improving the content of the book.
The authors will gratefully accept all critical comments from readers.

Chapter I TESTING TELESCOPES

§ 1. Introduction
Telescopes are the main instruments of every astronomical observatory, including the educational one. With the help of telescopes, students observe the Sun and the phenomena occurring on it, the Moon and its topography, the planets and some of their satellites, the diverse world of stars, open and globular clusters, diffuse nebulae, the Milky Way and galaxies.
Based on direct telescopic observations and on photographs taken with large telescopes, the teacher can create in students vivid natural-scientific ideas about the structure of the world around them and, on this basis, form firm materialistic convictions.
Starting observations at the school astronomical observatory, the teacher should be well aware of the possibilities of telescopic optics, various practical methods for testing it and establishing its main characteristics. The fuller and deeper the teacher's knowledge of telescopes, the better he will be able to organize astronomical observations, the more fruitful the work of the students will be and the more convincing the results of the observations will appear before them.
In particular, it is important for an astronomy teacher to know a brief theory of the telescope, be familiar with the most common optical systems and telescope settings, and also have a fairly complete knowledge of eyepieces and various telescope accessories. At the same time, he must know the main characteristics, as well as the advantages and disadvantages of small telescopes intended for school and institute educational astronomical observatories, have good skills in handling such telescopes and be able to realistically assess their capabilities when organizing observations.
The effectiveness of the work of an astronomical observatory depends not only on its equipment with various equipment and, in particular, on the optical power of the telescopes available on it, but also on the degree of preparedness of observers. Only a qualified observer, who has good skills in handling the telescope at his disposal and who knows its main characteristics and capabilities, is able to obtain the maximum possible information on this telescope.
Therefore, the teacher faces the important task of preparing activists who are able to make good observations that require endurance, careful execution, great attention and time.
Without the creation of a group of qualified observers, it is impossible to count on the widespread continuous functioning of the school observatory and on its great return in the education and upbringing of all other students.
In this regard, it is not enough for the teacher to know the telescopes themselves and their capabilities, he must also possess a thoughtful and expressive explanation method that does not go far beyond school curricula and textbooks and is based on the knowledge of students obtained in the study of physics, astronomy and mathematics.
At the same time, special attention should be paid to the applied nature of the reported information about telescopes, so that the capabilities of the latter are revealed in the process of carrying out the planned observations and manifest themselves in the results obtained.
Taking into account the above requirements, the first chapter of the book includes theoretical information about telescopes in the amount necessary for making well-thought-out observations, as well as descriptions of rational practical methods for testing and establishing their various characteristics, taking into account the knowledge and capabilities of students.

§ 2. Determination of the main characteristics of telescope optics
In order to deeply understand the possibilities of telescope optics, one should first give some optical data on the human eye - the main "tool" of students in most educational astronomical observations. Let us dwell on its characteristics such as extreme sensitivity and visual acuity, illustrating their content on examples of observations of celestial objects.
Under the limiting (threshold) sensitivity of the eye is understood the minimum luminous flux that can still be perceived by an eye fully adapted to the darkness.
Convenient objects for determining the limiting sensitivity of the eye are groups of stars of different magnitudes with carefully measured magnitudes. In a good state of the atmosphere, a cloudless sky on a moonless night far from the city, one can observe stars up to the 6th magnitude. However, this is not the limit. High in the mountains, where the atmosphere is especially clean and transparent, stars up to the 8th magnitude become visible.
An experienced observer must know the limits of his eyes and be able to determine the state of transparency of the atmosphere from observations of the stars. To do this, you need to study well the standard generally accepted in astronomy - the North Polar row (Fig. 1, a) and take it as a rule: before carrying out telescopic observations, you first need to determine with the naked eye the stars visible at the limit from this series and establish the state of the atmosphere from them.
Rice. 1. Map of the North Polar Range:
a - for observations with the naked eye; b - with binoculars or a small telescope; c - medium telescope.
The data obtained is recorded in the observation log. All this requires observation, memory, develops the habit of eye assessments and accustoms to accuracy - these qualities are very useful for the observer.
Visual acuity is understood as the ability of the eye to distinguish closely spaced objects or luminous points. Doctors have found that the average sharpness of a normal human eye is 1 minute of arc. These data were obtained by examining bright, well-lit objects and point light sources under laboratory conditions.
When observing stars - much less bright objects - visual acuity is somewhat reduced and is about 3 minutes of arc or more. So, having normal vision, it is easy to notice that near Mizar - the middle star in the handle of the Ursa Major bucket - there is a weak star Alkor. Far from everyone succeeds in establishing the duality of e Lyra with the naked eye. The angular distance between Mizar and Alcor is 1 Г48", and between the components ei and e2 of Lyra - 3"28".
Let us now consider how the telescope expands the possibilities of human vision, and analyze these possibilities.
A telescope is an afocal optical system that converts a beam of parallel beams with a cross section D into a beam of parallel beams with a cross section d. This is clearly seen in the example of the beam path in a refractor (Fig. 2), where the lens intercepts parallel beams coming from a distant star and focuses them to a point in the focal plane. Further, the rays diverge, enter the eyepiece and exit it as a parallel beam of smaller diameter. The beams then enter the eye and are focused to a point at the bottom of the eyeball.
If the diameter of the pupil of the human eye is equal to the diameter of the parallel beam emerging from the eyepiece, then all the rays collected by the objective will enter the eye. Therefore, in this case, the ratio of the areas of the telescope lens and the pupil of the human eye expresses the multiplicity of the increase in the light flux, falling
If we assume that the pupil diameter is 6 mm (in complete darkness it even reaches 7 - 8 mm), then a school refractor with a lens diameter of 60 mm can send 100 times more light energy into the eye than the naked eye perceives. As a result, with such a telescope, stars can become visible, sending us light fluxes 100 times smaller than the light fluxes from stars visible at the limit with the naked eye.
According to Pogson's formula, a hundredfold increase in illumination (luminous flux) corresponds to 5 star magnitudes:
The above formula makes it possible to estimate the penetrating power, which is the most important characteristic of a telescope. The penetrating power is determined by the limiting magnitude (m) of the faintest star that can still be seen with a given telescope under the best atmospheric conditions. Since neither the loss of light during the passage of the optics nor the darkening of the sky background in the field of view of the telescope is taken into account in the above formula, it is approximate.
A more accurate value of the penetrating power of a telescope can be calculated using the following empirical formula, which summarizes the results of observations of stars with instruments of different diameters:
where D is the diameter of the lens, expressed in millimeters.
For orientation purposes, Table 1 shows the approximate values ​​of the penetrating power of telescopes, calculated using the empirical formula (1).
The real penetrating power of the telescope can be determined by observing the stars of the Northern Polar series (Fig. 1.6, c). To do this, guided by table 1 or empirical formula (1), set the approximate value of the penetrating power of the telescope. Further, from the given maps (Fig. 1.6, c), stars with somewhat larger and somewhat smaller magnitudes are selected. Carefully copy all the stars of greater brilliance and all selected ones. In this way, a star chart is made, carefully studied, and observations are made. The absence of "extra" stars on the map contributes to the rapid identification of the telescopic picture and the establishment of the stellar magnitudes of the visible stars. Follow-up observations are made on subsequent evenings. If the weather and the transparency of the atmosphere improve, then it becomes possible to see and identify fainter stars.
The magnitude of the faintest star found in this way determines the real penetrating power of the telescope used. The results obtained are recorded in the observation log. From them one can judge the state of the atmosphere and the conditions for observing other luminaries.
The second most important characteristic of a telescope is its resolution b, which is understood as the minimum angle between two stars seen separately. In theoretical optics, it is proved that with an ideal lens in visible light L = 5.5-10-7 m, it is still possible to resolve a binary star if the angular distance between its components is equal to the angle
where D is the lens diameter in millimeters. (...)
Rice. 3. Diffraction patterns of close stellar pairs with different angular distances of the components.
It is also instructive to carry out telescopic observations of bright stellar pairs with the lens apertured. As the telescope's inlet is gradually diaphragmed, the diffraction disks of the stars increase, merge and merge into a single diffraction disk of larger diameter, but with much lower brightness.
When conducting such studies, attention should be paid to the quality of telescopic images, which are determined by the state of the atmosphere.
Atmospheric disturbances should be observed with a well-aligned telescope (preferably a reflector), examining diffraction images of bright stars at high magnifications. It is known from optics that with a monochromatic light flux, 83.8% of the energy transmitted through the lens is concentrated in the central diffraction disk, 7.2% in the first ring, 2.8% in the second, 1.5% in the third, and 1.5% in the fourth ring. - 0.9%, etc.
Since the incoming radiation from stars is not monochromatic, but consists of different wavelengths, the diffraction rings are colored and blurred. The clarity of ring images can be improved by using filters, especially narrow-band filters. However, due to the decrease in energy from ring to ring and the increase in their areas, already the third ring becomes inconspicuous.
This should be kept in mind when estimating the state of the atmosphere from visible diffraction patterns of observed stars. When making such observations, you can use the Pickering scale, according to which the best images are rated with a score of 10, and very poor ones with a score of 1.
We give a description of this scale (Fig. 4).
1. Images of stars are undulated and smeared so that their diameters are, on average, twice the size of the third diffraction ring.
2. The image is undulating and slightly out of the third diffraction ring.
3. The image does not go beyond the third diffraction ring. The image brightness increases towards the center.
4. From time to time, the central diffraction disk of the star is visible with short arcs appearing around.
5. The diffraction disk is visible all the time, and short arcs are often visible.
6. The diffraction disk and short arcs are visible all the time.
7. Arcs move around a clearly visible disk.
8. Rings with gaps move around a clearly defined disk,
9. The diffraction ring closest to the disk is motionless.
10. All diffraction rings are stationary.
Points 1 - 3 characterize the poor state of the atmosphere for astronomical observations, 4 - 5 - mediocre, 6 - 7 - good, 8 - 10 - excellent.
The third important characteristic of a telescope is its lens aperture, which is equal to the square of the ratio of the lens diameter
to its focal length (...)

§ 3. Checking the quality of telescope optics
The practical value of any telescope as an observational instrument is determined not only by its size, but also by the quality of its optics, i.e., the degree of perfection of its optical system and the quality of the lens. An important role is played by the quality of the eyepieces attached to the telescope, as well as the completeness of their set.
The lens is the most critical part of the telescope. Unfortunately, even the most advanced telescopic lenses have a number of drawbacks due to both purely technical reasons and the nature of light. The most important of these are chromatic and spherical aberration, coma and astigmatism. In addition, fast lenses suffer to varying degrees from field curvature and distortion.
The teacher needs to know about the main optical shortcomings of the most commonly used types of telescopes, expressively and clearly demonstrate these shortcomings and be able to reduce them to some extent.
Let us describe successively the most important optical shortcomings of telescopes, consider in what types of small telescopes and to what extent they manifest themselves, and indicate the simplest ways to highlight, display and reduce them.
The main obstacle that prevented the improvement of the refractor telescope for a long time was chromatic (color) aberration, i.e., the inability of a collecting lens to collect all light rays with different wavelengths at one point. Chromatic aberration is caused by the unequal refraction of light rays of different wavelengths (red rays are refracted more weakly than yellow ones, and yellow rays are weaker than blue ones).
Chromatic aberration is especially pronounced in telescopes with single-lens fast lenses. If such a telescope is pointed at a bright star, then at a certain position of the eyepiece
you can see a bright purple speck surrounded by a colored halo with a blurred red outer ring. As the eyepiece extends, the color of the central spot will gradually change to blue, then green, yellow, orange, and finally red. In the latter case, a colored halo with a purple ring border will be visible around the red spot.
If you look at the planet through such a telescope, the picture will be very blurry, with iridescent stains.
Two-lens lenses that are largely free of chromatic aberration are called achromatic. The relative aperture of a refractor with an achromatic lens is usually 715 or more (for school refracting telescopes, it leaves 7o, which somewhat degrades the image quality).
However, an achromatic lens is not completely free from chromatic aberration and converges well only rays of certain wavelengths. In this regard, the objectives are achromatized in accordance with their purpose; visual - in relation to the rays that act most strongly on the eye, photographic - for the rays that act most strongly on the photographic emulsion. In particular, the lenses of school refractors are visual in their purpose.
The presence of residual chromatic aberration in school refractors can be judged on the basis of observations with very high magnifications of diffraction images of bright stars, quickly changing the following filters: yellow-green, red, blue. It is possible to ensure a quick change of light filters by using disk or sliding frames, described in
§ 20 of the book "School Astronomical Observatory"1. The changes in the diffraction patterns observed in this case indicate that not all rays are equally focused.
The elimination of chromatic aberration is more successfully solved in three-lens apochromatic objectives. However, it has not yet been possible to completely destroy it in any lens objectives.
A reflex lens does not refract light rays. Therefore, these lenses are completely free from chromatic aberration. In this way, reflex lenses compare favorably with lenses.
Another major disadvantage of telescopic lenses is spherical aberration. It manifests itself in the fact that monochromatic rays running parallel to the optical axis are focused at different distances from the lens, depending on which zone they have passed through. So, in a single lens, the rays that have passed near its center are focused furthest, and the closest - those that have passed through the edge zone.
This can be easily seen if a telescope with a single-lens objective is directed at a bright star and observed with two diaphragms: one of them should highlight the flux passing through the central zone, and the second, made in the form of a ring, should transmit the rays of the edge zone. Observations should be carried out with light filters, if possible, with narrow bandwidths. When using the first aperture, a sharp image of the star is obtained at a slightly larger extension of the eyepiece than when using the second aperture, which confirms the presence of spherical aberration.
In complex lenses, spherical aberration, together with chromatic aberration, is reduced to the required limit by selecting lenses of a certain thickness, curvature, and types of glass used.
[ The remnants of uncorrected spherical aberration in complex lens telescopic objectives can be detected using (the apertures described above, observing diffraction patterns from bright stars at high magnifications. When studying visual lenses, yellow-green filters should be used, and when studying photographic lenses, blue.
! There is no spherical aberration in mirror parabolic (more precisely, paraboloidal) lenses, since the lenses | reduce to one point the entire beam of rays traveling parallel to the optical axis. Spherical mirrors have spherical aberration, and it is the greater, the larger and brighter the mirror itself.
For small mirrors with small luminosity (with a relative aperture of less than 1: 8), the spherical surface differs little from the paraboloidal one - as a result, the spherical aberration is small.
The presence of residual spherical aberration can be detected by the method described above, using different diaphragms. Although mirror lenses are free from chromatic aberration, filters should be used to better diagnose spherical aberration, because the color of the observed diffraction patterns at different apertures is not the same, which can lead to misunderstandings.
Let us now consider the aberrations that arise when rays pass obliquely to the optical axis of the objective. These include: coma, astigmatism, field curvature, distortion.
With visual observations, one should follow the first two aberrations - coma and astigmatism, and study them practically by observing the stars.
The coma manifests itself in the fact that the image of the star away from the optical axis of the objective takes the form of a blurry asymmetric spot with a displaced core and a characteristic tail (Fig. 6). Astigmatism, on the other hand, consists in the fact that the lens collects an inclined beam of light from the star not into one common focus, but into two mutually perpendicular segments AB and CD, located in different planes and at different distances from the lens (Fig. 7).
Rice. 6. Formation of coma in oblique rays. The circle outlines the field near the optical axis, where the coma is insignificant.
With good alignment in the telescope tube of a low-aperture objective and with a small field of view of the eyepiece, it is difficult to notice both aberrations mentioned above. They can be clearly seen if, for the purpose of training, the telescope is somewhat misaligned by turning the lens through a certain angle. Such an operation is useful for all observers, and especially for those who build their telescopes, because sooner or later they are bound to face alignment issues, and it will be much better if they act consciously.
To misalign the reflector, simply loosen and tighten the two opposite screws holding the mirror.
In a refractor, this is more difficult to do. In order not to spoil the thread, you should glue a transition ring truncated at an angle from cardboard and insert it with one side into the telescope tube, and put the lens on the other.
If you look at the stars through a misaligned telescope, they will all appear tailed. The reason for this is coma (Fig. 6). If, however, a diaphragm with a small central hole is put on the telescope inlet and the eyepiece is moved back and forth, then one can see how the stars are stretched into bright segments AB, then turn into ellipses of different compression, circles, and again into segments CD and ellipses (Fig. 7).
Coma and astigmatism are eliminated by turning the lens. As it is easy to understand, the axis of rotation during adjustment will be perpendicular to the direction. If the tail lengthens when the mirror adjusting screw is turned, then the screw must be rotated in the opposite direction. The final fine-tuning during adjustment should be carried out with a short-focus eyepiece at high magnifications so that the diffraction rings are clearly visible.
If the telescope lens is of high quality and the optics are aligned correctly, then the out-of-focus images of the star, when viewed through a refractor, will look like a small light disk surrounded by a system of colored concentric diffraction rings (Fig. 8, al). In this case, the patterns of prefocal and extrafocal images will be exactly the same (Fig. 8, a 2, 3).
Out-of-focus images of a star will have the same appearance when viewed through a reflector, only instead of a central bright disk, a dark spot will be seen, which is a shadow from an auxiliary mirror or a diagonal total reflection prism.
The inaccuracy of the telescope alignment will affect the concentricity of the diffraction rings, and they themselves will take an elongated shape (Fig. 8, b 1, 2, 3, 4). When focusing, the star will appear not as a sharply defined bright disk, but as a slightly blurred bright spot with a weak tail thrown to the side (coma effect). If the indicated effect is caused by a really inaccurate adjustment of the telescope, then the matter can be easily corrected, it is enough just to change its position somewhat in the desired direction by acting with the adjusting screws of the lens (mirror) frame. It is much worse if the reason lies in the astigmatism of the lens itself or (in the case of a Newton reflector) in the poor quality of the auxiliary diagonal mirror. In this case, the drawback can be eliminated only by grinding and repolishing the defective optical surfaces.
From out-of-focus images of a star, other shortcomings of the telescopic lens, if any, can be easily detected. For example, the difference in the sizes of the corresponding diffraction rings of the prefocal and extrafocal images of a star indicates the presence of spherical aberration, and the difference in their chromaticity indicates significant chromatism (for linear
call lens); the uneven distribution density of the rings and their different intensities indicate the zoning of the lens, and the irregular shape of the rings indicates local more or less significant deviations of the optical surface from the ideal.
If all the listed disadvantages revealed by the picture of out-of-focus images of a star are small, then they can be put up with. Specular objectives of amateur telescopes that have successfully passed the preliminary Foucault shadow test, as a rule, have an impeccable optical surface and withstand tests on out-of-focus star images perfectly.
Calculations and practice show that when the optics are perfectly aligned, coma and astigmatism have little effect on visual observations when low-aperture objectives (less than 1:10) are used. This applies equally to photographic observations, when luminaries with relatively small angular sizes (planets, the Sun, the Moon) are photographed with the same lenses.
Coma and astigmatism greatly spoil images when photographing large areas of the starry sky with parabolic mirrors or two-lens lenses. Distortion increases sharply with fast lenses.
The table below gives an idea of ​​the growth of coma and astigmatism depending on the angular deviations from the optical axis for parabolic reflectors of different luminosity.
Rice. 9. Curvature of the field of view and images of stars in its focal plane (with correction of all other aberrations).
tism, but there is a curvature of the field. If you take a picture of a large area of ​​the starry sky with such a lens and at the same time focus on the central zone, then as you retreat to the edges of the field, the sharpness of the images of stars will deteriorate. And vice versa, if focusing is performed on the stars located at the edges of the field, then the sharpness of the images of stars will deteriorate in the center.
In order to obtain a photograph sharp throughout the field with such a lens, the film must be bent in accordance with the curvature of the field of sharp images of the lens itself.
The curvature of the field is also eliminated with the help of a plano-convex Piazzi-Smith lens, which turns the curved wave front into a flat one.
The curvature of the field can be most simply reduced by aperture of the lens. From the practice of photography it is known that with a decrease in the aperture, the depth of field increases - as a result, clear images of stars are obtained over the entire field of a flat plate. However, it should be remembered that aperture greatly reduces the optical power of the telescope, and in order for faint stars to appear on the plate, the exposure time must be significantly increased.
Distortion manifests itself in the fact that the lens builds an image that is not proportional to the original, but with some deviations from it. As a result, when photographing a square, its image may turn out with sides concave inward or convex outward (pincushion and barrel distortion).
Examining any lens for distortion is very simple: to do this, you need to greatly aperture it so that only a very small central part remains uncovered. Coma, astigmatism and curvature of the field with such a diaphragm will be eliminated and distortion can be observed in its purest form
If you take pictures of rectangular grilles, window openings, doors with such a lens, then, by examining the negatives, it is easy to establish the type of distortion inherent in this lens.
The distortion of the finished lens cannot be eliminated or reduced. It is taken into account in the study of photographs, especially when carrying out astrometric work.

§ 4. Eyepieces and limiting magnifications of the telescope
The eyepiece set is a necessary addition to the telescope. Earlier we have already clarified (§ 2) the purpose of the eyepiece in a magnifying telescopic system. Now it is necessary to dwell on the main characteristics and design features of various eyepieces. Leaving aside the Galilean eyepiece from one diverging lens, which has not been used in astronomical practice for a long time, let us immediately turn to special astronomical eyepieces.
Historically, the first astronomical eyepiece, which immediately replaced the Galilean eyepiece, was the Kepler eyepiece from a single short-focus lens. Possessing a much larger field of view in comparison with Galileo's eyepiece, in combination with the long-focus refractors common at that time, it produced fairly clear and slightly colored images. However, later the Kepler eyepiece was superseded by the more advanced Huygens and Ramsden eyepieces, which are still found today. The most commonly used astronomical eyepieces at present are the Kellner achromatic eyepiece and the Abbe orthoscopic eyepiece. Figure 11 shows the arrangement of these eyepieces.
The Huygens and Ramsden eyepieces are most simply arranged. Each of them is composed of two plano-convex converging lenses. The front one (facing the objective) is called the field lens, and the back one (facing the observer's eye) is called the eye lens. In the Huygens eyepiece (Fig. 12), both lenses face the objective with their convex surfaces, and if f \ and / 2 are the focal lengths of the lenses, and d is the distance between them, then the relationship must be satisfied: (...)