Lexell's Comet
| Discovery | |
|---|---|
| Discovered by | Charles Messier |
| Discovery date | June 14, 1770 |
| Designations | |
| 1770, Lexell's Comet | |
D/1770 L1, popularly known as Lexell's Comet after its orbit computer Anders Johan Lexell, was a comet discovered by the great astronomer Charles Messier in June 1770. It is notable for having passed closer to the Earth than any other comet in recorded history, approaching to a distance of only 0.0146 astronomical units (about 1357155 miles).[1]
Discovery
The comet was discovered on June 14 in the constellation Sagittarius by Messier, who had just completed an observation of Jupiter and was examining several nebulae.[1] At this time it was very faint, but his observations over the course of the next few days showed that it rapidly grew in size, its coma reaching 27 minutes in size by 24 June: by this time it was of magnitude 2. The comet was also noted by several other astronomers.
Close approach to Earth
On July 1, the comet passed just 0.0146 AU from Earth, a tiny distance in astronomical terms. Messier measured the coma as 2°23' across, while an English astronomer noted it crossing over 42° of sky in 24 hours; he described the nucleus as being as large as Jupiter, "surrounded with a coma of silver light, the brightest part of which was as large as the moon's orb".[1]
Messier was also the last astronomer to see the comet as it moved away from the Sun, on October 3.
Orbit
A number of orbital calculations were made, some indicating a perihelion date (the date of the closest approach to the Sun) of August 9-10, and some a date of 13-14, depending on whether the orbital solutions were parabolic or elliptical. Anders Johan Lexell made four separate sets of calculations over a period of several years and deduced an orbital period of 5.58 years.[1] Lexell also identified that despite this short-period orbit, the comet was unlikely to have been seen previously because its orbit had been radically altered by the gravitational forces of Jupiter.[2]
The comet was never seen again. Lexell argued that a subsequent interaction with Jupiter had further perturbed its orbit, either placing it too far from the Earth to be seen or perhaps ejecting it from the Solar System altogether.