A significant contribution to the development of astrospectroscopy was made by a compatriot, Sekka Giovanni Donati (1826-1873), whose name is usually associated with the comet he discovered in 1858 and named after him as a bright and very beautiful comet. Donati was the first to receive her spectrum and to identify the stripes and lines observed in it. He studied the spectra of the Sun, stars, the solar chromosphere, and the crown, as well as the polar lights.
William Heggins (1824-1910) established the similarity of the spectra of many stars with the spectrum of the Sun. He showed that light is emitted by its glowing surface, absorbed after that by the gases of the solar atmosphere. It became clear why the lines of elements in the spectrum of the Sun and stars are usually dark, rather than bright. Haggins first obtained and studied the spectra of gas nebulae, consisting of individual radiation lines. This proved that they are gas nebulae.
Heggins first studied the spectrum of a new star, namely the new Northern Crown, which broke out in 1866, and discovered the existence of an expanding gas shell around the star. He was one of the first to use the Doppler principle of Fizo (often referred to as the Doppler effect) to determine the velocities of the stars by the beam of vision.
Shortly before that, in 1842, the Austrian physicist Christian Doppler (1803-1853) theoretically proved that the frequency of sound and light oscillations, perceived by the observer, depends on the speed of approach or removal of their source. The tone height of the locomotive, for example, changes sharply (downwards) when the approaching train passes by us and begins to move away.
The outstanding French physicist Armand Hippolyte Louis Fizeau (1819-1896) in 1848 tested this phenomenon for light rays in the laboratory. He also proposed to use it to determine the velocities of stars by the beam of vision, the so-called radial velocities - the displacement of the spectral lines to the violet end of the spectrum (in the case of approaching source) or to red (in the case of its removal). In 1868 Heggins measured the radial velocity of Sirius in this way. It turned out that it was approaching the ground at a speed of about 8 km/s.
The consistent application of the Doppler-Phozo principle in astronomy has led to many remarkable discoveries. In 1889, the director of the Harvard Observatory (USA), Edward Charles Pickering (1846-1919) found a split line in the spectrum of Mitzara - the famous star of the 2nd-star size in the tail of the Big Bear. Lines with a certain period were shifted and then moved apart. Pickering realized that this is probably a close double system: its stars are so close to each other that they can not be distinguished in any telescope. However, spectral analysis makes it possible to do so. Since the velocities of both stars of the pair are directed in different directions, they can be determined using the Doppler - Fizo principle (and, of course, also the period of the stars' rotation in the system).
In 1900 astronomer Aristarchus Apollo (1854-1934) used this principle to determine the velocities and rotation periods of the planets. If to put a slot of a spectrograph along the equator of a planet, spectral lines will receive an inclination (one edge of a planet to our approaches, and another - leaves). Applying this method to the rings of Saturn, Belopolsky proved that the sections of the ring are circulating the planet under the laws of Kepler, and therefore consist of many separate, unrelated small particles, as suggested by the theoretical considerations, James Clerk Maxwell (1831-1879) and Sophia Vasilevna Kovalevskaya (1850-1891).
Simultaneously with Belopolsky, the same result was obtained by the American astronomer James Edward Keeler (1857-1900) and the French astronomer Henri Delander (1853-1948).
About a year before these studies Belopolsky discovered a periodic change in the radial velocities of cepheids. At the same time, Moscow physicist Nikolai Alekseevich Umov (1846-1915) expressed the idea that in this case, scientists are not dealing with a double system, as they believed, and with the pulsation of the star.
Meanwhile, astrospectroscopy was making more and more progress. In 1890, the Harvard Astronomical Observatory released a large catalog of star spectra, containing 10350 stars up to the 8th stellar magnitude and up to 25 south declination. It was dedicated to the memory of Henry Draper (1837-1882), an American astronomer (medical specialty) and pioneer of photography in astronomy. In 1872 he received the first photograph of the star spectrum (spectrogram), and later - the spectra of bright stars, moon, planets, comets, and nebulae. After the first volume of the catalog was published, additions to it were published more than once. The total number of studied spectra of stars reached 350 thousand.
To be continued in the next part https://zen.yandex.ru/media/id/5d92f1673d873600b11d9f29/as-astrophysics-was-conceived-part-3-5d92f9dcc31e4900b16af4c8