Comet of the Week: 9P/Tempel 1

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Special Topic: Past Spacecraft Missions

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Special Topic: The Tunguska Event and Other Recent Impacts

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Special Topic: Orbits and Future Returns

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JUNE 22, 1978: U.S. Naval Observatory astronomer James Christy discovers Charon, Pluto’s first-known moon. Charon, the discovery of which would be confirmed with a series of transit and occultation events between it and Pluto that began in 1995, provided a major step in our understanding of Pluto’s size and physical nature. Pluto, its system of …

Perihelion: 2020 June 25.85, q = 0.337 AU  In the early 19th Century the idea that comets might return to the inner solar system on a regular basis was still a bit of a novelty. This had been successfully demonstrated by the British astronomer Edmond Halley when the comet that now bears his name returned …

“Ice and Stone 2020” participants have undoubtedly noticed that I have often discussed how this-or-that comet or asteroid will be returning to the inner solar system or passing by Earth at some point in the future, and perhaps have wondered how such things are determined. In principle, the processes by which such events are calculated …

JUNE 14, 1770: The renowned French comet hunter Charles Messier discovers a moderately bright comet in Sagittarius. 2½ weeks later this comet passed just 0.015 AU from Earth, the closest confirmed cometary approach to Earth in history. The comet, named after Swedish mathematician Anders Lexell, who computed its orbit, was later perturbed into a much …

Perihelion: 2001 May 24.52, q = 0.779 AU  At the beginning of the 21st Century the discovery of comets and near-Earth asteroids was dominated by the first of the comprehensive sky surveys, the LIncoln Near-Earth Asteroid Research (LINEAR) program run by MIT’s Lincoln Laboratory and based at White Sands Missile Range in New Mexico, that …

Ever since the Italian astronomer Galileo Galilei turned his primitive telescope towards the moon on November 30, 1609 and saw them for the first time, we’ve known that the moon is covered with craters. These come in all sizes, from very large ones several hundred km across down to meter-size and smaller. For a long …