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C/1965 S1 (Ikeya-Seki)

Roger Lynds photo of C/1965 S1 exposed on 1965 October 29
Copyright © 1965 by Roger Lynds

This photo was taken by Roger Lynds at Kitt Peak, Arizona, on the morning of 1965 October 29. It was a 4-minute exposure. The two stars to the left of the comet's head are Delta and Eta Corvi (magnitude 3.0 and 4.3, respectively), while the star a little ways up and just right of the tail is Gamma Corvi (magnitude 2.6). The tail extends into Crater in this picture, with the length being about 17°. (Special thanks to Jeannette Barnes (NOAO/Tucson) for relaying my request to use this picture to Roger Lynds).


     Kaoru Ikeya and Tsutomu Seki independently discovered this comet on 1965 September 18.8, within about 15 minutes of each other. It was then just west of Alpha Hydrae. The magnitude was estimated as 8, and the comet was described as diffuse, with a condensation. The first confirmation was obtained on September 19.79, when the Smithsonian Astrophysical Observatory station at Woomera, Australia, obtained a photograph showing the comet at magnitude 8.

Historical Highlights

  • Comet quickly recognized as a sungrazer and brightened rapidly. It reached magnitude 5.5 by October 1 and magnitude 2 by October 15. On the latter date the tail was 5° long.
  • The comet was closest to the Sun (perihelion) on October 21 (0.008 AU).
  • Became visible in broad daylight on October 21 to anyone who blocked the sun with their hand. Maximum magnitude may have been around -10 or -11.
  • Japanese astronomers using a coronagraph on Mount Norikura said the comet was seen to disrupt into three pieces just 30 minutes prior to perihelion.
  • F. Moriyama and T. Hirayama photo of C/1965 S1 exposed on 1965 October 21
    Copyright © 1965 by F. Moriyama and T. Hirayama

    This photo was taken by F. Moriyama and T. Hirayama (Tokyo Astronomical Observatory, Mitaka, Japan) at the Norikura Corona Station on 1965 October 21. They used a 12-cm coronagraph and Fuji Panchroprocess plates behind a Mazda VG1B color filter. This was a 4-second exposure.

  • Comet's tail was longest at the end of October and early November when observers reported lengths of 20° to 25°.
  • Two definite nuclei were photographed on November 4, with a third suspected.
  • Comet last definitely detected on January 14, 1966, although images were suspected on Baker-Nunn plates exposed on February 12.
  • The orbital period is 880 years. There is a chance this was a return of the great comet of 1106, which was seen in broad daylight in Europe.
  • cometography.com