Russian astronomer, who claimed to have discovered volcano-like activity on the Moon. His sightings of apparent gaseous emissions from the lunar surface challenged the long-held theory that the Moon is a dead and inert celestial body.

In 1931 Kozyrev joined the staff of the Pulkovo Astronomical Observatory, near Leningrad (St. Petersburg), where he studied the planets and auroral phenomena. These studies gained him distinction, but he was imprisoned by the Stalin regime in 1937 and was not released until 1948.

In 1954 Kozyrev made a much-disputed report of an aurora, similar to the Earth's Aurora Borealis, on the planet Venus. The existence of such an aurora would mean that Venus has a magnetic field much like Earth's, and the study of Venerian phenomena would thus provide much new information on geomagnetic storms. (The U.S. space probe Mariner 10, passing within 3,600 miles 【5,800 km】 of Venus in February 1974, found no detectable magnetic field.)

While investigating the lunar crater Alphonsus in 1958, Kozyrev reported a reddish mist covering part of it for a short time. He interpreted this as a volcanic eruption and confirmed his observations the following year, but his conclusion that volcanic activity was the cause of the disturbance has been disputed by astronomers. Nonetheless, his observations led to a new focus in lunar research for a time.

In 1963 Kozyrev startled astronomers with his spectroscopic discovery of hydrogen in the thin atmosphere of Mercury. This gas should have escaped Mercury's light gravitational field long ago. From further studies Kozyrev concluded that the hydrogen comes from the Sun in the form of hydrogen nuclei.