Discovery circumstances are available for most planetary satellites, selected comets, and numbered asteroids. These data include the discovery date, location of discovery, and one or more names credited with the discovery. In addition, recently named asteroids include their IAU naming citation.

Planets (and Pluto)

Most of the planets (including the Earth's moon) have been known to mankind since ancient times. The planets beyond Saturn were discovered in more recent times.

Uranus (1781)

The discovery of Uranus was unexpected. William Herschel in England thought he was looking at a strange comet in 1781. Through his telescope, the best in the world at that time, the object was seen to have a sharply defined disk and no tail. Subsequent positional measurements showed the orbit to be far away and virtually circular; and thus, a planet. The size of the known planetary solar system had instantly doubled.

Neptune (1846)

The discovery of Neptune is regarded as a triumph of celestial mechanics. Neptune's existence was inferred from its effect upon the orbit of Uranus. Using that effect, its position was predicted by Urbain Jean Joseph Le Verrier in France and by John Couch Adams in England. As a result of Le Verrier's prediction, Neptune was quickly found by Johann Galle of the Berlin Observatory in 1846.

Pluto (1930)

In contrast to the discoveries of Uranus and of Neptune, the discovery of Pluto was the result of a dedicated, diligent photographic search. In 1930, Clyde Tombaugh of the Lowell Observatory, detected the slight motion of the tiny planet among the greatly brighter background stars.

The stories of the planetary discoveries are described in "Planets Beyond" by Mark Littmann (1988, Wiley and Sons) and in "Planet Quest" by Ken Croswell (1997, Harcourt Brace & Company). The story of Neptune is preserved in the file of letters that were exchanged among the numerous participants. Synopses of these letters are available from a web-site by Nicholas Kollerstrom.

Planetary Satellites

Planetary satellite discovery circumstances are available in a separate table which includes the satellite provisional designation, IAU number (if assigned), IAU name (if assigned), year of discovery, a list of discoverers, and references (where known).

Comets and Asteroids

Comet and asteroid discovery circumstances are available using our small-body browser. Discovery data are available only for numbered asteroids and selected comets. These data include the date of discovery, who discovered the object, and where it was discovered. In addition, for recently named asteroids, the citation issued for their name is available.