Comet Ikeya-Seki, formally designated as C/1967 Y1, is a retrograde non-periodic comet discovered by Kaoru Ikeya and Tsutomu Seki on 1967. It is the second comet discovered together by the two Japanese astronomers after C/1965 S1.
Discovery and observations.
C/1967 Y1 was the 14th comet discovered in 1967 when both Kaoru Ikeya and Tsutomu Seki spotted it as a 9th-magnitude object on the evening of December 28th. The comet's position remained circumpolar throughout its last perihelion, thus giving astronomers a rare opportunity to observe it all night long.
By 25 February 1968, the comet reached an apparent magnitude of 7.1 and developed a very faint tail. Photometric spectroscopy of the comet's tail together with comets C/1968 L1 and C/1968 N1 has shown its forward scattering to be gray in the 3500–6300 Å spectrum, in contrast to the reddening of the dust tail seen in other comets. The comet was last observed from the Kitt Peak Observatory on 4 November 1969.