After Galileo sent a telescope to the sky for the first time in 1609, the possibilities of astronomical observations increased very strongly. This year was the beginning of a new era in science - the era of telescopic astronomy.
Galileo's telescope on present concepts was imperfect, however to contemporaries it seemed to be a miracle from miracles. Everyone, having looked into it, could be convinced that the Moon is a complex world, in many respects similar to the Earth, that around Jupiter four small satellites address, as well as the Moon around the Earth. All this made us think about the complexity of the Universe, its materiality and the multitude of inhabited worlds.
The invention of the telescope, as well as most of the great discoveries, was not accidental, it was prepared by all the previous progress in science and technology. In the XVI century, craftsmen learned to make spectacle lenses, and from here was one step to the telescope and microscope.
The telescope has three main purposes:
- Collect radiation from celestial luminaries on the receiving device (eye, photographic plate, spectrograph, etc.);
- To build an image of an object or a certain part of the sky in its focal plane;
- Help to distinguish between objects, the location at a close angular distance from each other and therefore indistinguishable by the naked eye.
The main optical part of the telescope is the lens, which collects light and builds an image of an object or a part of the sky. The lens connects to the receiver, the tube. The mechanical construction that carries the tube and ensures its pointing to the sky is called amount. If the receiver of light is an eye (for visual observations), it is necessary to use an eyepiece, in which the image built by the lens is considered. An eyepiece is not necessary for photographic, photovoltaic, and spectral observations. The photographic plate, the inlet diaphragm of the electrophotometer, the gap of the spectrograph, etc., are installed directly in the focal plane of the telescope.
Innovations
At the end of XIX and especially in XX century the character of astronomical science underwent organic changes. The center of gravity of research has moved to the field of astrophysics and starry astronomy. The main subject of research was the physical characteristics of the Sun, planets, stars, and star systems. New radiation receivers appeared - a photographic plate and a photocell. Spectroscopy has become widely used. As a result, the requirements for telescopes have also changed.
For astrophysical researches it is desirable that optics of a telescope did not impose any restrictions on an accessible range of lengths of waves: the terrestrial atmosphere limits it too much already. Meanwhile, the glass from which the lenses are made absorbs ultraviolet and infrared radiation. Photographic immunizations and photocells are sensitive in a wider spectral area than the eye, and therefore chromatic aberration when working with these receivers affects more strongly.
How to look through the telescope correctly
In order to monitor the celestial luminaire in the equator, it is enough to turn it only around the polar axis in the direction of the clockwise angle growth, as the inclination of the luminaire remains unchanged. This rotation is performed automatically by the clockwork. There are several types of equatorial mountings. Moderate-diameter telescopes (up to 50 to 100 cm) are often mounted on a "German" mount, in which the polar axis and declination axis form a parallactic head resting on a column. On the axis of declination, on one side of the column, there is a pipe, and on the other - a counterweight to balance its weight. The "English" mount differs from the German one in that the polar axis is supported by the ends on two columns, northern and southern, which gives it additional stability. Sometimes in the English mount, the polar axis replaces the quadrangular frame so that the pipe is inside the frame. Such a design does not allow to direct the instrument to the polar sky. If the northern (upper) bearing of the polar axis is made in the form of a horseshoe, there will be no such restriction. Finally, it is possible to remove the northern column and the bearing at all. Then you will get an "American" mount or a "fork".
The clock mechanism does not always work only, and at reception of photos with the long expositions reaching sometimes many hours, it is necessary to watch correctness of an orientation of a telescope and from time to time to correct it. This process is called a guide. Guiding is carried out with the help of a guide - a small auxiliary telescope mounted on a common mount with the main telescope.