153P/Ikeya–Zhang

Comet Ikeya–Zhang (Japanese, Chinese: 池谷-張彗星, officially designated 153P/Ikeya–Zhang) is a comet discovered independently by two astronomers from Japan and China in 2002. It has by far the longest orbital period of the numbered periodic comets. It was last observed in October 2002 when it was about Template:Convert from the Sun.Template:R

Discovery and observations

On 1 February 2002, Chinese astronomer Zhang Daqing from Kaifeng discovered a new comet in the constellation Cetus, and reported it to the IAU. He found that Japanese astronomer Kaoru Ikeya had discovered it earlier than he had, as the time of sunset is earlier than China. According to tradition, since they discovered the new comet independently, the comet was named after both of them. The comet was initially designated as C/2002 C1 (Ikeya–Zhang).

The comet was observed in 1661, 341 years earlier, by Polish astronomer Johannes Hevelius.Template:RTemplate:Sfn A bright comet had also been recorded by Chinese astronomers in 1661.Template:Sfn Further research by Ichiro Hasegawa and Shuichi Nakano concluded that historical comets recorded in A.D. 877Template:Sfn and 1273Template:Sfn were likely previous apparitions of Ikeya–Zhang as well.Template:R

The permanent designation "153P" was given to the comet. It has the longest known orbital period of any periodic comet (366.51 years). Its orbital speed around the Sun varies from Template:Cvt at perihelion to Template:Cvt at aphelion.Template:Efn

The comet passed perihelion on 18 March 2002, and with apparent magnitude 2.9. With a multi-hundred year orbit involving asymmetric outgassing the next perihelion passage is expected between 2362–2363. During March–April 2002, protons from the comet tail may have been detected by the Cassini–Huygens spacecraft. This data suggested the comet tail had a length greater than Template:Convert, making it the longest yet detected.Template:R

Orbit

The orbital paths of three comets, outlined in turquoise, against the orbits of Jupiter, Saturn, Uranus and Neptune, outlined in green

The orbits of three periodic comets, Halley, Borrelly and Ikeya–Zhang, set against the orbits of the outer planets. Ikeya–Zhang is to the right.

See also

• Johannes Hevelius
• List of Solar System objects by greatest aphelion

External links

• Template:JPL Small Body
• 153P/Ikeya–Zhang (2002)