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.

Ikeya–Zhang on April 1, 2002
Discovered byKaoru Ikeya, Zhang Daqing
Discovery dateFebruary 1, 2002
C/2002 C1, C/1661 C1
Orbital characteristics A
EpochOctober 13, 2002
Aphelion101.92 AU
Perihelion0.50714 AU
Semi-major axis51.213 AU
Orbital period366.51 yr[1]
Max. orbital speed59 km/s (2002)
Min. orbital speed0.29 km/s[a]
Last perihelionMarch 18, 2002[1][2]
January 29, 1661[3]
Next perihelionSeptember 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 observed in 1661, 341 years earlier, by Polish astronomer Johannes Hevelius.[5] 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.[a]

The comet passed perihelion on March 18, 2002, and with apparent magnitude 3.5, it became the brightest comet since 1997. With a multi-hundred year orbit involving asymmetric outgassing the next perihelion passage is expected between 2362–2363.

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 alsoEdit


  1. ^ a b v = 42.1219 1/r − 0.5/a, where r is the distance from the Sun, and a is the major semi-axis.


  1. ^ a b "JPL Small-Body Database Browser: 153P/Ikeya-Zhang". Jet Propulsion Laboratory. Retrieved 2011-04-20. 2002-10-02 last obs (arc 341.6 yr)
  2. ^ "153P/Ikeya-Zhang Orbit". Minor Planet Center.
  3. ^ a b Syuichi Nakano (2002-08-13). "153P/Ikeya-Zhang". OAA Computing and Minor Planet Sections. Retrieved 2009-10-04.
  4. ^ "Horizons Batch for 153P/Ikeya–Zhang (90001064) on 2363-Mar-14" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons. Retrieved 2021-04-10. (JPL#74/Soln.date: 2020-Jun-17)
  5. ^ Green, D. (2004). "Assessment of early-modern observations of comets and supernovae: Focus on pre-telescopic European astrometric and physical data" (PDF). Durham theses. Durham University. pp. 213–228.

External linksEdit

Numbered comets
153P/Ikeya–Zhang Next