Which comet has come closest to the Earth?

Comet IRAS-Araki-Alcock was the 7th comet discovered in 1983. This figure includes an FES image of the comet showing its diffuse tail and the LWR spectrum depicting the molecular emission lines of sulfur (S2) and hydroxyl (OH).

The comet, IRAS-Araki-Alcock visited us in 1983 and was originally detected by the Infrared Astronomical Satellite, although this did not get into the press until several days later on April 27, 1983 when the English amateur astronomer Alcock and the Japanese amateur Araki independently discovered it and brought it to everyone's attention. Some Swedish astronomers at the Uppsala University had also detected it about the same time.

It was discovered on April 27, and it made its closest approach to the Earth on May 11, coming to within 3 million miles ( 4.5 million kilometers)!!! It was so close that, even its brightness was diffused over a large area of the sky making it a faint object. At its closest approach it moved 60 degrees across the sky in less than a day!

It didn't have much of a tail, as many of the comets do that come closest to Earth. We see them almost head-on with little or no tail. This makes them hard to detect until they are almost right on top of us! If there is, out there in space, a comet with the Earth's name written on it as a Doomsday Comet, we will probably not detect it until a few weeks before the 'event'.

Pretty spooky!

Here is a list of the 20 Closest Comet Passes to the Earth prepared by the IAU Minor Planets Center. The dates of closest approach are given in Terrestrial Time (TT), although at the precision of this table they can be considered to be in Universal Time (UT). For comparison, the mean distance of the moon is 0.0026 AU = 384400 km = 238900 miles. (1 AU is approximately the mean distance of the earth from the sun = 149597870 km = 92955810 miles.)

Distance  Date (TT)       Permanent designation 

 0.0151   1770 July  1.7      D/1770 L1 (Lexell)
 0.0229   1366 Oct. 26.4    55P/1366 U1 (Tempel-Tuttle)
 0.0312   1983 May  11.5      C/1983 H1 (IRAS-Araki-Alcock)
 0.0334    837 Apr. 10.5     1P/837 F1 (Halley)
 0.0366   1805 Dec.  9.9     3D/1805 V1 (Biela)
 0.0390   1743 Feb.  8.9      C/1743 C1
 0.0394   1927 June 26.8     7P/Pons-Winnecke
 0.0437   1702 Apr. 20.2      C/1702 H1
 0.0617   1930 May  31.7    73P/1930 J1 (Schwassmann-Wachmann 3)
 0.0628   1983 June 12.8      C/1983 J1 (Sugano-Saigusa-Fujikawa)
 0.0682   1760 Jan.  8.2      C/1760 A1 (Great comet)
 0.0839   1853 Apr. 29.1      C/1853 G1 (Schweizer)
 0.0879   1797 Aug. 16.5      C/1797 P1 (Bouvard-Herschel)
 0.0884    374 Apr.  1.9     1P/374 E1 (Halley)
 0.0898    607 Apr. 19.2     1P/607 H1 (Halley)
 0.0934   1763 Sept.23.7      C/1763 S1 (Messier)
 0.0964   1864 Aug.  8.4      C/1864 N1 (Tempel)
 0.0982   1862 July  4.6      C/1862 N1 (Schmidt)
 0.1018   1996 Mar. 25.3      C/1996 B2 (Hyakutake)
 0.1019   1961 Nov. 15.2      C/1961 T1 (Seki)

Note: This list is complete for comets discovered after 1700 that approached the earth to within 0.1020 AU. It also includes a number of well-documented earlier approaches by periodic comets. C/1491 B1 allegedly came to within 0.0094 AU on 1491 Feb. 20.0 TT, but the orbit of this comet is very uncertain. Additional (uncertain) ancient approaches are given in `Close Encounters and Collisions of Comets with the Earth' by Z. Sekanina and D. K. Yeomans (Astron. J. 89, 154-161).


Copyright 1997 Dr. Sten Odenwald

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