Types of telescopes. Astronomical instruments and observations with them
Currently, a variety of telescopes can be found on store shelves. Modern manufacturers take care of their customers and try to improve each model, gradually eliminating the shortcomings of each and them.
In general, such devices are still arranged according to one similar scheme. What is the general arrangement of a telescope? More on this later.
Pipe
The main part of the instrument is the pipe. A lens is placed in it, into which rays of light fall further. Lenses come in different types at once. These are reflectors, catadioptric lenses and refractors. Each type has its pros and cons, which users study before buying and, relying on them, make a choice.
The main components of each telescope: tube and eyepiece
In addition to the pipe, the instrument also has a finder. We can say that this is a miniature spyglass that connects to the main pipe. In this case, an increase of 6-10 times is observed. This part of the device is necessary for preliminary aiming at the object of observation.
Eyepiece
Another important part of any telescope is the eyepiece. It is through this interchangeable part of the tool that the user observes. The shorter this part, the greater the magnification can be, but the smaller the angle of view. It is for this reason that it is best to purchase several different eyepieces with the device at once. For example, with fixed and variable focus.
Mounting, filters and other details
Mounting also comes in several types. As a rule, the telescope is mounted on a tripod, which has two rotary axes. And there are also additional "mounts" on the telescope, which are worth mentioning. First of all, these are filters. They are needed by astronomers for a variety of purposes. But for beginners, it is not necessary to purchase them.
True, if the user plans to admire the moon, then you will need a special lunar filter that will protect your eyes from too bright a picture. There are also special filters that are able to eliminate the interfering light of city lights, but they are quite expensive. In order to view objects in the correct position, diagonal mirrors are also useful, which, depending on the type, are capable of deflecting rays by 45 or 90 degrees.
The structure of the telescope
In the 20th century, astronomy took many steps in the study of our universe, but these steps would not have been possible without the use of such sophisticated instruments as telescopes, which have a history of more than one hundred years. The evolution of the telescope took place in several stages, and it is about them that I will try to tell.
Since ancient times, humanity has been drawn to find out what is there, in the sky, beyond the Earth and invisible to the human eye. The greatest scientists of antiquity, such as Leonardo da Vinci, Galileo Galilei, attempted to create a device that allows you to look into the depths of space and lift the veil of the mystery of the universe. Since then, there have been many discoveries in the field of astronomy and astrophysics. Everyone knows what a telescope is, but not everyone knows how long ago and by whom the first telescope was invented, and how it was arranged.
Telescope - an instrument designed to observe celestial bodies.
In particular, a telescope is understood as an optical telescopic system not necessarily used for astronomical purposes.
There are telescopes for all ranges of the electromagnetic spectrum:
b optical telescopes
b radio telescopes
b x-ray telescopes
gamma-ray telescopes
Optical telescopes
A telescope is a tube (solid, frame or truss) mounted on a mount equipped with axes for pointing at the object of observation and tracking it. A visual telescope has a lens and an eyepiece. The rear focal plane of the objective is aligned with the front focal plane of the eyepiece. Instead of an eyepiece, a photographic film or a matrix radiation detector can be placed in the focal plane of the objective. In this case, the telescope lens, from the point of view of optics, is a photographic lens. The telescope is focused using a focuser (focused device). telescope space astronomy
According to their optical design, most telescopes are divided into:
ü Lens (refractors or diopters) - a lens or lens system is used as a lens.
b Mirror (reflectors or catoptric) - a concave mirror is used as a lens.
b Mirror-lens telescopes (catadioptric) - a spherical mirror is used as an objective, and a lens, lens system or meniscus serves to compensate for aberrations.
A telescope is an astronomical optical instrument designed to observe celestial bodies.
The telescope has an eyepiece, a lens or a main mirror and a special tube that is attached to the mount, which, in turn, contains axes, due to which the pointing at the object of observation takes place.
In 1609, Galileo Galilei assembled the first optical telescope in human history. (Read about it on our website: Who created the first telescope?).
Modern telescopes come in several types.
Reflector (mirror) telescopes
If we give them the most simplified description, then these are devices that have a special concave mirror that collects light and focuses it. The advantages of such telescopes include ease of manufacture, good quality optics. The main disadvantage is a little more care and maintenance than other types of telescopes.
Well, now in more detail about reflector telescopes.
A reflector is a telescope with a mirror lens that forms an image by reflecting light from a mirrored surface. Reflectors are mainly used for sky photography, photoelectric and spectral studies, and they are used less often for visual observations.
Reflectors have some advantages over refractors (lens telescopes), because they do not have chromatic aberration (coloration of images); the main mirror is easier to make larger than the lens objective. If the mirror is not spherical, but parabolic, then the spherical shape can be reduced to zero. aberration(blurring of the edges or middle of the image). The manufacture of mirrors is easier and cheaper than lens objectives, which makes it possible to increase the diameter of the objective, and hence the resolving power of the telescope. From a ready-made set of mirrors, amateur astronomers can create a homemade "Newtonian" reflector. The advantage due to which the system has gained popularity among amateurs is the ease of manufacture of mirrors (the main mirror in the case of small relative apertures is a sphere; a flat mirror can be small).
Newtonian reflector
It was invented in 1662. His telescope was the first mirror telescope. In reflectors, the large mirror is called the main mirror. Photographic plates can be placed in the plane of the main mirror to photograph celestial objects.
In Newton's system, the lens is a concave parabolic mirror, from which the reflected rays are directed by a small flat mirror into an eyepiece located on the side of the tube.
Picture: Reflection of signals coming from different directions.
Gregory system reflector
Rays from the main concave parabolic mirror are directed to a small concave elliptical mirror, which reflects them into an eyepiece placed in the central hole of the main mirror. Since the elliptical mirror is located behind the focus of the main mirror, the image is upright, while in the Newtonian system it is inverted. The presence of a second mirror increases the focal length and thus enables a large magnification.
Cassegrain reflector
Here the secondary mirror is hyperbolic. It is installed in front of the focus of the main mirror and allows you to make the reflector tube shorter. The main mirror is parabolic, there is no spherical aberration here, but there is a coma (the image of a point takes the form of an asymmetric scattering spot) - this limits the field of view of the reflector.
Reflector of the Lomonosov-Herschel system
Here, unlike the Newtonian reflector, the main mirror is tilted so that the image is focused near the telescope's entrance hole, where the eyepiece is placed. This system made it possible to exclude intermediate mirrors and light losses in them.
Ritchey-Chrétien reflector
This system is an improved version of the Cassegrain system. The main mirror is a concave hyperbolic one, and the auxiliary mirror is a convex hyperbolic one. The eyepiece is installed in the central hole of the hyperbolic mirror.
Recently, this system has been widely used.
There are other reflex systems: Schwarzschild, Maksutov and Schmidt (mirror-lens systems), Mersen, Nessmit.
Lack of reflectors
Their pipes are open to air currents that spoil the surface of the mirrors. From temperature fluctuations and mechanical loads, the shape of the mirrors slightly changes, and because of this, visibility worsens.
One of the largest reflectors is located at the Mount Palomar Astronomical Observatory in the United States. Its mirror has a diameter of 5 m. The world's largest astronomical reflector (6 m) is located in the Special Astrophysical Observatory in the North Caucasus.
Refractor telescope (lens telescope)
Refractors- These are telescopes that have a lens objective that forms an image of objects by refraction of light rays.
This is a classic long tube known to everyone in the form of a telescope with a large lens (objective) at one end and an eyepiece at the other. Refractors are used for visual, photographic, spectral and other observations.
Refractors are usually built according to the Kepler system. The angular vision of these telescopes is small, not exceeding 2º. The lens is usually two-lens.
Lenses in small refractor lenses are usually glued to reduce glare and light loss. The surfaces of the lenses are subjected to a special treatment (optical coating), as a result of which a thin transparent film is formed on the glass, which significantly reduces light loss due to reflection.
The world's largest refractor at the Yerkes Astronomical Observatory in the United States has a lens diameter of 1.02 m. A refractor with a lens diameter of 0.65 m is installed at the Pulkovo Observatory.
Mirror-lens telescopes
A mirror-lens telescope is designed to photograph large areas of the sky. It was invented in 1929 by the German optician B. Schmidt. The main details here are a spherical mirror and a Schmidt correction plate installed in the center of the mirror's curvature. Due to this position of the correction plate, all beams of rays passing through it from different parts of the sky are equal in relation to the mirror, as a result of which the telescope is free from aberrations of optical systems. The spherical aberration of the mirror is corrected by a correction plate, the central part of which acts as a weak positive lens and the outer part as a weak negative lens. The focal surface, on which the image of a section of the sky is formed, has the shape of a sphere, the radius of curvature of which is equal to the focal length. The focal surface can be flattened using a Piazzi Smith lens.
disadvantage mirror-lens telescopes is a significant length of the tube, twice the focal length of the telescope. To eliminate this shortcoming, a number of modifications have been proposed, including the use of a second (additional) convex mirror, bringing the correction plate closer to the main mirror, etc.
The largest Schmidt telescopes are installed at the Tautenburg Astronomical Observatory in the GDR (D = 1.37m, A = 1:3), the Mount Palomar Astronomical Observatory in the USA (D = 1.22 m, A = 1:2.5) and at Byurakan Astrophysical Observatory of the Academy of Sciences of the Armenian SSR (D = 1.00 m, A = 1:2, 1:3).
radio telescopes
They are used to study space objects in the radio range. The main elements of radio telescopes are receiving antenna and radiometer- sensitive radio receiver and receiving equipment. Since the radio range is much wider than the optical range, various designs of radio telescopes are used to detect radio emission, depending on the range.
When combined into a single network of several single telescopes located in different parts of the globe, one speaks of very long baseline radio interferometry (VLBI). An example of such a network is the American VLBA (Very Long Baseline Array) system. From 1997 to 2003, the Japanese orbiting radio telescope HALCA (Highly Advanced Laboratory for Communications and Astronomy), included in the network of VLBA telescopes, operated, which significantly improved the resolution of the entire network.
The Russian orbiting radio telescope Radioastron is planned to be used as one of the elements of the giant interferometer.
Space telescopes (astronomical satellites)
They are designed to carry out astronomical observations from space. The need for this type of observatory arose due to the fact that the earth's atmosphere delays the gamma, x-ray and ultraviolet radiation of space objects, as well as most of the infrared.
Space telescopes are equipped with devices for collecting and focusing radiation, as well as data conversion and transmission systems, an orientation system, and sometimes propulsion systems.
X-ray telescopes
Designed to observe distant objects in the X-ray spectrum. To operate such telescopes, it is usually necessary to raise them above the Earth's atmosphere, which is opaque to X-rays. Therefore, telescopes are placed on high-altitude rockets or on artificial earth satellites.
In the picture: X-ray Telescope - Position Sensitive (ART-P). It was created in the Department of High Energy Astrophysics of the Space Research Institute of the USSR Academy of Sciences (Moscow).
A telescope is an instrument used to observe distant objects. Translated from Greek, "telescope" means "far away" and "observe".
What is a telescope for?
Someone thinks that the telescope enlarges objects, and someone believes that it brings them closer. Both of them are wrong. The main task of the telescope is to obtain information about the observed object by collecting electromagnetic radiation.
Electromagnetic radiation is not only visible light. Electromagnetic waves also include radio waves, terahertz and infrared radiation, ultraviolet, x-ray and gamma radiation. Telescopes are designed for all ranges of the electromagnetic spectrum.
optical telescope
The main task of the telescope is to increase the angle of view, or visible angular dimension remote object.
The angular dimension is the angle between the lines connecting the diametrically opposite points of the observed object and the observer's eye. The farther away the observed object is, the smaller the angle of view will be.
Let's mentally connect two opposite points of the tower crane's boom with our eye with straight lines. The resulting angle will be the angle of view, or angular size. Let's do the same experiment with a crane standing in a neighboring yard. The angular size in this case will be much smaller than in the previous one. All objects appear to us large or small depending on their angular dimensions. And the farther the object is located, the smaller its angular size will be.
An optical telescope is a system that changes the angle of inclination of the optical axis of a parallel beam of light. Such an optical system is called afocal. Its peculiarity lies in the fact that light rays enter it in a parallel beam, and exit in the same parallel beam, but at different angles, different from the viewing angles with the naked eye.
The afocal system consists of an objective and an eyepiece. The lens is directed at the observed object, and the eyepiece is turned to the observer's eye. They are positioned so that the front focus of the eyepiece coincides with the back focus of the objective.
An optical telescope collects and focuses electromagnetic radiation in the visible spectrum. If only lenses are used in its design, such a telescope is called refractor , or a diopter telescope. If only mirrors, then it is called reflector , or a catapric telescope. There are optical telescopes of a mixed type, which include both lenses and mirrors. They are called mirror-lens , or catadioptric.
The "classic" spyglass, which was used back in the days of the sailing fleet, consisted of a lens and an eyepiece. The lens was a positive converging lens that produced a real image of the object. The enlarged image was viewed by the observer through the eyepiece - a negative diverging lens.
The drawings of the simplest optical telescope were created by Leonardo da Vinci in 1509. The Dutch optician is considered the author of the telescope John Lippershey who demonstrated his invention in The Hague in 1608.
Galileo Galilei turned a telescope into a telescope in 1609. The device he created had a lens and an eyepiece and gave a 3-fold increase. Galileo later created a telescope with 8x magnification. But his designs were very large. So, the diameter of the lens of a telescope with a 32x magnification was 4.5 m, and the telescope itself had a length of about a meter.
The name "telescope" for Galileo's instruments was suggested by the Greek mathematician Giovanni Demisiani in 1611
It was Galileo who first sent a telescope into the sky and saw spots on the Sun, mountains and craters on the Moon, examined the stars in the Milky Way.
Galileo's tube is an example of the simplest refractor telescope. The lens is a converging lens. In the focal plane (perpendicular to the optical axis and passing through the focus), a reduced image of the object in question is obtained. The eyepiece, which is a diverging lens, makes it possible to see an enlarged image. Galileo's tube gives a slight magnification of a distant object. It is not used in modern telescopes, but a similar scheme is used in theater binoculars.
In 1611 a German scientist Johannes Kepler came up with a better design. Instead of a diverging lens, he placed a converging lens in the eyepiece. The image came out inverted. This created inconvenience for the observation of terrestrial objects, but for space objects it was quite acceptable. In such a telescope, there was an intermediate image behind the focus of the lens. A measuring scale or photographic plate could be built into it. This type of telescope immediately found its application in astronomy.
AT reflecting telescopes instead of a lens, a concave mirror serves as a collecting element, the rear focal plane of which is aligned with the front focal plane of the eyepiece.
The mirror telescope was invented by Isaac Newton in 1667. In its design, the main mirror collects parallel light rays. So that the observer does not block the luminous flux, a flat mirror is placed in the path of the reflected rays, which deflects them from the optical axis. The image is viewed through the eyepiece.
Instead of an eyepiece, you can place a film or photosensitive matrix, which converts the image projected onto it into an analog electrical signal or into digital data.
AT mirror-lens telescopes the lens is a spherical mirror, and the lens system compensates for aberrations - image errors caused by the deviation of the light beam from the ideal direction. They exist in any real optical system. As a result of aberrations, the image of a point is blurred and becomes fuzzy.
Optical telescopes are used by astronomers to observe the heavenly bodies.
But the Universe sends to Earth not only light. Radio waves, X-rays and gamma rays come to us from space.
Radio telescope
This telescope is designed to receive radio waves emitted by celestial objects in the Solar System, Galaxy and Megagalaxy, to determine their spatial structure, coordinates, radiation intensity and spectrum. Its main elements are a receiving antenna and a very sensitive receiver - a radiometer.
The antenna is capable of receiving millimeter, centimeter, decimeter and meter waves. Most often, this is a parabolic mirror reflector, in the focus of which is the irradiator. This is a device in which radio emission directed by a mirror is collected. Further, this radiation is transmitted to the input of the radiometer, where it is amplified and converted into a form convenient for registration. This can be an analog signal that is recorded by a recorder, or a digital signal that is recorded on a hard disk.
To build an image of the observed object, the radio telescope measures the radiation energy (brightness) at each of its points.
space telescopes
The Earth's atmosphere transmits optical radiation, infrared and radio radiation. And ultraviolet and X-ray radiation is delayed by the atmosphere. Therefore, they can be observed only from space, installed on artificial Earth satellites, space rockets or orbital stations.
X-ray telescopes are designed to observe objects in the x-ray spectrum, so they are installed on artificial earth satellites or space rockets, since the earth's atmosphere does not transmit such rays.
X-rays are emitted by stars, galaxy clusters and black holes.
The function of the lens in an X-ray telescope is performed by an X-ray mirror. Since X-rays pass almost completely through the material or are absorbed by it, ordinary mirrors cannot be used in X-ray telescopes. Therefore, to focus the beams, grazing or oblique incidence mirrors made of metals are most often used.
In addition to X-ray telescopes, ultraviolet telescopes operating in ultraviolet light.
Gamma-ray telescopes
Not all gamma-ray telescopes are placed on space objects. There are ground-based telescopes that study ultrahigh-energy cosmic gamma radiation. But how to fix gamma radiation on the Earth's surface if it is absorbed by the atmosphere? It turns out that superhigh-energy cosmic gamma-ray photons, having entered the atmosphere, “knock out” secondary fast electrons from atoms, which are sources of photons. Arises, which is fixed by a telescope located on Earth.
The principle of a telescope is not to magnify objects, but to collect light. The larger the size of the main light-collecting element - a lens or a mirror, the more light will enter it. It is important that it is the total amount of light collected that ultimately determines the level of detail visible - whether it be a distant landscape or the rings of Saturn. While the magnification, or power, of the telescope is also important, it is not critical to achieving the level of detail.
Telescopes are constantly changing and improving, but the principle of operation remains the same.
Telescope collects and concentrates light
The larger the convex lens or concave mirror, the more light enters it. And the more light enters, the more distant objects it allows you to see. The human eye has its own convex lens (crystalline lens), but this lens is very small, so it collects quite a bit of light. The telescope allows you to see more precisely because its mirror is able to collect more light than the human eye.
A telescope focuses light beams and creates an image
In order to create a clear image, the lenses and mirrors of the telescope collect the captured rays into one point - into focus. If the light is not collected at one point, the image will be blurry.
Types of telescopes
Telescopes can be divided according to the way they work with light into "lens", "mirror" and combined - mirror-lens telescopes.
Refractors are refractive telescopes. The light in such a telescope is collected using a biconvex lens (in fact, it is the lens of the telescope). Among amateur instruments, the most common achromats are usually two-lens, but there are also more complex ones. An achromatic refractor consists of two lenses - a converging and a diverging one, which allows you to compensate for spherical and chromatic aberrations - in other words, distortions in the flow of light when passing through the lens.
A bit of history:
Galileo's refractor (invented in 1609) used two lenses to collect as much starlight as possible. and let the human eye see it. Light passing through a spherical mirror forms an image. Galileo's spherical lens makes the picture fuzzy. In addition, such a lens decomposes light into color components, due to which a blurry colored area forms around the luminous object. Therefore, the spherical convex collects starlight, and the concave lens following it turns the collected light rays back into parallel ones, which allows you to restore clarity and clarity to the observed image.
Keppler refractor (1611)
Any spherical lens refracts light rays, defocuses them and blurs the picture. A spherical Keppler lens has less curvature and a longer focal length than a Galilean lens. Therefore, the focus points of rays passing through such a lens are closer to each other, which reduces, but does not completely eliminate, image distortion. In fact, Keppler himself did not create such a telescope, but the improvements he proposed had a strong influence on the further development of refractors.
Achromatic refractor
The achromatic refractor is based on the Keppler telescope, but instead of one spherical lens, it uses two lenses of different curvatures. Light passing through these two lenses is focused at one point, i.e. this method avoids both chromatic and spherical aberration.
- Telescope Sturman F70076
A simple and lightweight refractor for beginners with a 50mm objective lens. Magnification - 18*,27*,60*,90*. It is completed with two eyepieces - 6 mm and 20 mm. Can be used as a pipe as it does not flip the image. On the azimuth bracket. - >Telescope Konus KJ-7
60 mm long-focus refractor telescope on a German (equatorial) mount. The maximum magnification is 120x. Suitable for children and novice astronomers. - Telescope MEADE NGC 70/700mm AZ
A classic refractor with a diameter of 70 mm and a maximum useful magnification of up to 250*. Comes with three eyepieces, a prism and a mount. Allows you to observe almost all the planets of the solar system and faint stars up to magnitude 11.3. - Telescope Synta Skywatcher 607AZ2
A classic refractor on an azimuth mount AZ-2 on an aluminum tripod and the possibility of microdimensional pointing of the telescope in height. Objective diameter 60 mm, maximum magnification 120x, penetrating power 11 (magnitudes). Weight 5 kg. - Telescope Synta Skywatcher 1025AZ3
Lightweight refractor with AZ-3 alt-azimuth mount on an aluminum tripod with microdimensional telescope pointing on both axes. Can be used as a telephoto lens for most SLR cameras to capture distant subjects. Objective diameter 100 mm, focal length 500 mm, penetrating power 12 (magnitudes). Weight 14 kg.
Reflector is any telescope whose objective consists only of mirrors. Reflectors are reflecting telescopes, and the image in such telescopes is on the other side of the optical system than in refractors.
A bit of history
Gregory's reflecting telescope (1663)
James Gregory introduced a completely new technology to telescope construction by inventing the telescope with a parabolic primary mirror. The image that can be observed in such a telescope is free from both spherical and chromatic aberrations.
Newton's reflector (1668)
Newton used a metal primary mirror to collect the light and a follower mirror to direct the light rays towards the eyepiece. Thus, it was possible to cope with chromatic aberration - after all, mirrors are used in this telescope instead of lenses. But the picture still turned out blurry due to the spherical curvature of the mirror.
Until now, a telescope made according to Newton's scheme is often called a reflector. Unfortunately, it is not free from aberrations either. Slightly away from the axis, coma (non-isoplanatism) is already beginning to appear - an aberration associated with the uneven increase in different annular aperture zones. The coma causes the diffuse spot to look like a projection of a cone - the sharpest and brightest part towards the center of the field of view, obtuse and rounded away from the center. The size of the scattering spot is proportional to the distance from the center of the field of view and is proportional to the square of the aperture diameter. Therefore, the manifestation of coma is especially strong in the so-called "fast" (high-aperture) Newtons at the edge of the field of view.
Newtonian telescopes are very popular today: they are very simple and cheap to manufacture, which means that the average price level for them is much lower than for the corresponding refractors. But the design itself imposes some limitations on such a telescope: distortions of the rays passing through a diagonal mirror noticeably worsen the resolution of such a telescope, and with an increase in the diameter of the objective, the length of the tube increases proportionally. As a result, the telescope becomes too large, and the field of view with a long tube becomes smaller. Actually, reflectors with a diameter of more than 15 cm are practically not produced, because. The disadvantages of such devices will be more than advantages.
- Telescope Synta Skywatcher 1309EQ2
Reflector with a 130 mm objective lens on an equatorial mount. Max magnification 260. Insight 13.3 - Telescope F800203M STURMAN
Reflector with a 200 mm objective lens on an equatorial mount. Supplied with two eyepieces, moon filter, tripod and viewfinders. - Telescope Meade Newton 6 LXD-75 f/5 with EC Remote
A classic Newtonian reflector with a lens diameter of 150 mm and a useful magnification of up to 400x. A telescope for astronomy enthusiasts who appreciate a large light diameter and large aperture. An electronically driven mount with hourly tracking allows long exposure astrophotography.
Mirror lens(catadioptric) telescopes use both lenses and mirrors, whereby their optical design achieves excellent high-resolution image quality, while the entire structure consists of very short portable optical tubes.
Telescope parameters
Diameter and magnification
When choosing a telescope, it is important to be aware of objective lens diameter, resolution, magnification, and quality of construction and components.
The amount of light collected by a telescope directly depends on diameter(D) primary mirror or lens. The amount of light passing through the lens is proportional to its area.
In addition to the diameter, the characteristic of the lens is important value relative bore(A), equal to the ratio of the diameter to the focal length (it is also called aperture ratio).
Relative Focus called the reciprocal of the relative aperture.
Permission- is the ability to display details - ie. the higher the resolution, the better the image. A high-resolution telescope is able to separate two distant near objects, while a low-resolution telescope will only see one, mixed of the two, object. Stars are point sources of light, so they are difficult to observe, and only the diffraction image of a star can be seen in a telescope as a disk with a ring of light around it. Officially, the maximum resolution of a visual telescope is the minimum angular gap between a pair of stars of the same brightness, when they are still visible at sufficient magnification and the absence of interference from the atmosphere separately. This value for good instruments is approximately equal to 120/D arcseconds, where D is the telescope aperture (diameter) in mm.
Magnifications telescope should lie in the range from D / 7 to 1.5D, where D is the aperture diameter of the telescope objective. That is, for a tube with a diameter of 100 mm, eyepieces must be selected so that they provide magnifications from 15x to 150x.
With a magnification numerically equal to the diameter of the lens, expressed in millimeters, the first signs of a diffraction pattern appear, and further increase in magnification will only worsen the image quality, preventing fine details from being distinguished. In addition, it is worth remembering the jitter of the telescope, atmospheric turbulence, etc. Therefore, when observing the Moon and planets, magnifications exceeding 1.4D - 1.7D are usually not used. In any case, a good instrument should "pull out" up to 1.5D without significant deterioration in image quality. Refractors do this best, and reflectors with their central shielding can no longer work confidently at such magnifications, therefore, it is not advisable to use them for observing the Moon and planets.
The upper limit of rational magnifications is determined empirically and is related to the influence of diffraction phenomena (with increasing magnification, the size of the exit pupil of the telescope decreases - its exit aperture). It turned out that the highest resolution is achieved with exit pupils less than 0.7 mm, and further increase in magnification does not lead to an increase in the number of details. On the contrary, a loose, cloudy and dim image creates the illusion of reduced detail. Large magnifications of 1.5D make sense as more comfortable, especially for people with visual impairments and only for bright contrasting objects.
The lower limit of a reasonable range of magnifications is determined by the fact that the ratio of the lens diameter to the exit pupil diameter (i.e., the diameter of the light beam emerging from the eyepiece) is equal to the ratio of their focal lengths, i.e. increase. If the diameter of the beam exiting the eyepiece exceeds the diameter of the observer's pupil, some of the rays will be cut off, and the observer's eye will see less light - and a smaller part of the image.
Thus, the following series of recommended magnifications 2D, 1.4D, 1D, 0.7D, D/7 emerges. A magnification of D/2..D/3 is useful for observing ordinary-sized clusters and dim nebulous objects.
mounts
Telescope mount- the part of the telescope on which its optical tube is fixed. Allows you to direct it to the observed region of the sky, ensures the stability of its installation in the working position, the convenience of performing various types of observations. The mount consists of a base (or column), two mutually perpendicular axes for turning the telescope tube, a drive and a system for measuring the angles of rotation.
AT equatorial mount the first axis is directed to the celestial pole and is called the polar (or hourly) axis, and the second lies in the plane of the equator and is called the declination axis; a telescope tube is attached to it. When the telescope is rotated around the 1st axis, its hour angle changes at a constant declination; when rotated around the 2nd axis, the declination changes at a constant hour angle. If the telescope is mounted on such a mount, tracking of a celestial body moving due to the apparent diurnal rotation of the sky is carried out by rotating the telescope at a constant speed around one polar axis.
AT azimuthal mount the first axis is vertical, and the second, carrying the pipe, lies in the horizon plane. The first axis is used to rotate the telescope in azimuth, the second - in height (zenith distance). When observing stars with a telescope mounted on an azimuth mount, it must be rotated continuously and with a high degree of accuracy around two axes simultaneously, and at speeds that vary according to a complex law.
Used photos from www.amazing-space.stsci.edu