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Comet Ikeya-Seki

Comet Ikeya-Seki


The Discovery of Comet Ikeya-Seki (C/1965 S1)

Comet Ikeya–Seki (C/1965 S1) was discovered independently by two Japanese astronomers on the morning September 18, 1965. At its time discovery, the comet was to the west of Alpha Hydrae and already less than 100,000,000 miles (161,000,000 km) from the Sun, which is slightly more than the distance between the Sun and the Earth.


Both of these young Japanese astronomers had previously discovered comets, but didn’t realize the importance of their most recent discovery until Dr. Leland E. Cunningham, of the Leuschner Observatory in Berkeley California, calculated the orbit and announced that Comet Ikeya-Seki would skim the surface of the Sun. Dr. Cunningham also announced that Ikeya-Seki had an orbit in keeping with a Kreutz Sungrazers—a theortical giant comet that broke apart centuries ago. Its fragments, including Ikeya-Seki, now orbit the Sun once every 600 to 1000 years. Many Kreutz sungrazers develop long dust tails, if they can survive their close encounter with the Sun. There were high hopes that Ikeya-Seki could survive due to the size of it nucleus, and become a spectacular naked-eye comet in 1965.


Comet Ikeya-Seki didn’t disappoint. It was one of the brightest comets in history.


Additional information about Ikeya-Seki (C/1965 S1)

Ikeya-Seki Comet
This photo of Ikeya-Seki was taken in 1966. Credit: © Roger Lynds/NOAO/AURA/NSF

As expected on October 21, 1965, Comet Ikeya-Seki passed fairly close to the Sun at a distance of 279,617 miles (450,000 km). Gas and dust exploded from the nucleus as the Sun took its toll. The comet flared to an apparent magnitude (brightnees) of -10. For comparison the apparent magnitude of Venus and the full Moon are -4.6 and -12.7, respectively. In plain English, Comet Ikeya-Seki was over 100 times as bright as Venus. It was the brightest comet since the Great Comet of 1882 (C/1882 R1, 1882 II, and 1882b).


Weather permitting, Comet Ikeya-Seki could be seen day-after-day just before sunrise. The tail, always pointing away from the Sun, would rise just before the Sun. The nucleus of the comet would rise minutes later. The tail curved slightly since the comet was slingshotting around the Sun at over 1,000,000 miles (1,610,000 km) an hour.


The tail grew to be 70,000,000 miles (113,000,000 km) long – two-thirds of the distance between Earth and the Sun. It was the fourth longest tail in recorded history—behind the Great Comets of 1680, 1811 and 1843. Its closest approach to Earth was roughly 80,000,000 miles (129,000,000 km).


During its close encounterwith the Sun, Comet Ikeya-Seki was observed breaking into three pieces. They were named C/1965 S1, C/1965 S1-A and C/1965 S1-B.


The orbit of Comet Ikeya-Seki and Comet Ikeya-Seki’s Return

The orbit of Comet Ikeya-Seki’s fragments have been calculated between 877 and 1056 years. Since its most recent visit to the inner solar system occurred in 1965, the next visit of its fragments will occur sometime between 2842 and 3021 CE.


No matter how much organic food we eat, those of us living today will never see Ikeya-Seki again. We're left with only spectacular photographs and memories.



Diagram ofComet Ikeya-Seki's orbital path by JPL


(on left) Orbit of Comet Ikeya-Seki (C/1965 S1) if solar system was seen top-down

(on right) Orbit of Comet Ikeya-Seki (C/1965 S1) compared to the ecliptic

Credit: Osamu Ajiki (AstroArts) modified by Ron Baalke (JPL)