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.

153P/Ikeya-Zhang

Ikeya–Zhang on April 1, 2002
Discovery
Discovered by	Kaoru Ikeya, Zhang Daqing
Discovery date	February 1, 2002
Alternative designations	C/2002 C1, C/1661 C1
Orbital characteristics A
Epoch	October 13, 2002
Aphelion	101.9200 AU
Perihelion	0.507141 AU
Semi-major axis	51.2136 AU
Eccentricity	0.990098
Orbital period	366.5101 yr[1]
Max. orbital speed	59 km/s (2002)
Min. orbital speed	0.29 km/s[lower-alpha 1] (2182-Nov-24)
Inclination	28.1199°
Last perihelion	March 18, 2002[1][2] January 29, 1661[3]
Next perihelion	September 1, 2362[3]

On February 1, 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 probably observed in 1661, 341 years earlier, by Polish astronomer Johannes Hevelius. A bright comet had also been recorded by Chinese astronomers in 1661.

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 59 km/s at perihelion to 0.29 km/s at aphelion.[lower-alpha 1]

The comet passed perihelion on March 18, 2002, and with apparent magnitude 3.5, it became the brightest comet since 1997.

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.