There are two comets named Ikeya–Seki: C/1965 S1 (this one), and C/1967 Y1, a.k.a. 1968 I, 1967n.

Comet Ikeya–Seki, formally designated C/1965 S1, 1965 VIII, and 1965f, was a long-period comet

Comet

A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...

 discovered independently by Kaoru Ikeya

Kaoru Ikeya

is a Japanese amateur astronomer who discovered a number of comets.As a young adult, Ikeya lived near Lake Hamana and worked for a piano factory. During his employment there, he made his first discovery in 1963 with an optical telescope he built himself within his low budget...

 and Tsutomu Seki

Tsutomu Seki

is a Japanese astronomer, born in Kōchi, Japan.He has discovered a number of comets, including the celebrated bright C/1965 S1 .He has also discovered a large number of asteroids, including the Amor asteroid 1992 JE and the Trojan asteroid .Many of his discoveries are named after famous sites in...

. First observed as a faint telescopic object on September 18, 1965, the first calculations of its orbit suggested that on October 21, it would pass just 450,000 km above the Sun

Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

's surface, and would probably become extremely bright.

Comets can defy all predictions, but Ikeya–Seki performed as expected. As it approached perihelion observers reported that it was clearly visible in the daytime sky next to the Sun. In Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, where it reached perihelion at local noon, it was seen shining at magnitude

Apparent magnitude

The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 −10. It proved to be one of the brightest comets seen in the last thousand years, and is sometimes known as the Great Comet

Great comet

A Great Comet is a comet that becomes exceptionally bright. There is no official definition; often the term will be attached to comets that become bright enough to be noticed by casual observers who are not actively looking for them, and become well known outside the astronomical community. Great...

 of 1965.

The comet was seen to break into three pieces just before its perihelion passage. The three pieces continued in almost identical orbits, and the comet re-appeared in the morning sky in late October, showing a very bright tail. By early 1966, it had faded from view as it receded into the outer solar system

Solar System

The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

.

Ikeya–Seki is a member of the Kreutz Sungrazers

Kreutz Sungrazers

The Kreutz Sungrazers are a family of sungrazing comets, characterized by orbits taking them extremely close to the Sun at perihelion. They are believed to be fragments of one large comet that broke up several centuries ago and are named for German astronomer Heinrich Kreutz, who first...

, which are suggested to be fragments of a large comet which broke up in 1106.