a scientific discipline that conducts investigations using astronomical instruments located outside the dense atmosphere. The effort to place observation instruments outside the atmosphere is connected with the fact that its transparency is limited to two relatively narrow spectrum regions: visible light (wavelengths of 3,000-7,500 A) and the radio-frequency band (1.25-30 m). Radiation of other wavelengths arriving from the sun and other astronomical objects is more or less absorbed, mainly by water vapor, carbon dioxide, and ozone. The absorption quickly decreases with increasing altitude above the earth’s surface, primarily because of decreased water vapor content. Terrestrial observations are also greatly hindered by atmospheric dust, clouds, and the refraction of light in thermally inhomogeneous regions, which causes flickering.
Extraterrestrial astronomical observations are carried out by means of rockets, relatively small earth satellites, and sometimes space probes. Using instruments placed in rockets, scientists obtain spectroheliograms—photographs of the sun in ultraviolet rays and in the spectral radiation lines of hydrogen and calcium. This method is of great interest for studying the active regions of the sun. Radiation spectra are also obtained of the sun in the ultraviolet and X-ray ranges of the spectrum, which permits study of the sun’s activity as well as the mechanism of its influence on the upper atmosphere of the earth. The long-wave and short-wave radiation of celestial bodies is measured with the aid of artificial earth satellites and space probes, including Elektron and Zond (USSR) and OSO and Solrad (USA); the sky in the ultraviolet and X-ray ranges of the spectrum is photographed with the aid of rockets and other devices.
Extraterrestrial investigations complement the results of terrestrial astronomical observations. Thus, the flight and landing experiments (first initiated by the USSR in 1959) for studying the physical characteristics of the moon, Mars, and Venus (cosmic devices of the Luna, Venera, and Zond series in the USSR and Surveyor, Lunar Orbiter, and Mariner series in the USA) have significantly broadened knowledge of the physical conditions on these celestial bodies. In this respect great importance is attached to observations made (first in 1969) by American astronauts on the surface of the moon and particularly to astronomical experiments carried out with the aid of such Soviet devices as the automatic probe Luna 16 and the mobile laboratory on the moon’s surface, Lunokhod 1 (since Nov. 18, 1970). The field of extra-terrestrial astronomy also includes research on the magnetic fields around celestial bodies and in interplanetary space and the study of corpuscular fluxes, cosmic rays, and the solid components of interplanetary substance. Taking samples of micrometeor particles and recording collisions with micro-meteor particles, which is widely carried out in the USSR and the USA, have given results substantially supplementing data that were obtained by studying large meteors that had fallen to earth and terrestrial deposits of micrometeor substance.
Extraterrestrial astronomy can include balloon astronomy, which uses large aerostats reaching altitudes of 30 km and higher for lifting astronomical instruments, including telescopes.
Extraterrestrial astronomy also includes the creation of extraterrestrial orbiting and lunar observatories. One of the first steps in this direction was the satellite Stargazer (USA); it was launched in December 1968 carrying a telescope that made it possible to photograph and obtain television images of celestial bodies and other astronomical objects.
M. G. KROSHKIN