The purpose of astrophysics is to study the physical nature and evolution of individual space objects, including the entire universe. Thus, astrophysics solves the most general problems of astronomy as a whole. Over the past decades, it has become a leading branch of astronomy. This does not mean that the role of such "classical" sections as celestial mechanics, astrometry, etc., is not being played. - The role of such "classical" sections as celestial mechanics, astrometry, etc., has diminished. On the contrary, the number and significance of works in traditional areas of astronomy are also growing, but in astrophysics, this growth is increasing faster. In general, astronomy develops harmoniously as a single science, and the direction of research in its various sections takes into account their mutual interests, including astrophysics. Thus, for example, the development of space research partially contributed to the emergence of a new section of celestial mechanics - astrodynamics. The construction of space models of the Universe places special demands on the "classical tasks" of astrometry, etc.
It is well known that astronomy has undergone several revolutions during its centuries-old history, which completely changed its character. One of the results of this process was the emergence and rapid development of astrophysics. Especially it was promoted by application of a telescope since the beginning of the XVII century, opening of the spectral analysis and invention of a photo in the XIX century, occurrence of photoelectric, radio astronomy and out of atmosphere methods of research in XX century. All this has unusually expanded the possibilities of observational or practical astrophysics and led to the fact that in the middle of the XX century, astronomy has become omni-wave, ie was able to extract information from any range of the electromagnetic radiation spectrum.
In parallel with the development of practical astrophysics methods, theoretical astrophysics has developed due to progress in physics and, in particular, the theory of radiation and the structure of the atom. Its purpose is to interpret the results of observations, set new research objectives, and substantiate practical astrophysics methods.
Both sections of astrophysics, in turn, are subdivided into more specific sections. As a rule, theoretical astrophysics is divided into objects of research: the physics of stars, the Sun, planets, nebulae, cosmic rays, cosmology, etc. The sections of practical astrophysics usually reflect some of the methods used: astrophotometry, astrospectrometry, astrophotography, colorimetry, etc.
Sections of astrophysics, the basis for the application of fundamentally new methods, which made up the era of astronomy, and, as a rule, include the relevant sections of theoretical astrophysics have received such names as radio astronomy, balloon astronomy, extra atmospheric astronomy (space research), X-ray astronomy, gamma-ray astronomy, neutrino astronomy.
Ground-based spectral studies
Let's consider the main types of spectral devices used in astronomy. For the first time spectra of stars and planets began to be observed in the last century by Italian astronomer Secchi. After his work, many astronomers started spectral analysis. At first, a visual spectroscopy was used, then the spectra were photographed, and now the photovoltaic recording of the spectrum is also used. Spectral instruments with photographic recording of the spectrum are usually called spectrographs, and with photovoltaic - spectrometers.
Currently, along with prism spectrographs and spectrometers, diffraction spectrometers are widely used. In these devices, instead of a prism, a diffraction lattice is a dispersing (i.e., decomposing into a spectrum) element. Reflective grids are the most commonly used.
Reflective grating is an aluminum mirror with parallel strokes. The distance between the strokes and their depth is comparable to a long wave. For example, diffraction gratings operating in the visible spectrum are often made with a stroke spacing of 1.66 microns (600 strokes per 1 mm). The strokes must be straight and parallel to each other over the entire surface of the grating, and the distance between them must remain constant with very high accuracy. The production of diffraction gratings is, therefore, the most difficult of the optical production.