21P/ Giacobini-Zinner Comet

Astronomical specifications: Discovery  December 20, 1900 Orbital characteristics: Distance from Sun   km Perihelion   (106 km) Aphelion   (106 km) Inclination   deg Eccentricity   Orbital periode rond Sun   days Main orbital speed   km/s Inclination to Sun equator   deg Number of moons   Rings   Physical characteristics: Dimensions   km Radius   km Surface area   km² Volume   106 km³ Mass   1024 kg Density   g/cm³ Equatorial surface gravity   m/s² Escape velocity   km/s Rotation period   days Surface temperature   K Axial tilt   deg Atmospheric composition

Michael Jäger image of 21p exposed on October 24, 1998

Discovery:

Historical Highlights:

• This comet was observed for nearly two months during its discovery apparition. During the latter days of 1900 December, observers estimated the comet's total magnitude as between 10.5 and 11, while the magnitude of the nuclear condensation was about 12. The coma was near one arc minute in diameter, and no tail was reported. The comet faded as January began and it was last seen on February 16.
• The comet was missed at the unfavorable 1920 return, but was next recovered on 1926 October 16 at Bergedorf. The precise position indicated the prediction for this return had been in error by only 5 days. The comet reached a maximum brightness of 11 and a maximum tail length of 2 arc minutes.
• First ever comet fly-by on Sep 02, 1985 by ICE probe. Closest approach on Sep 11, 1985 at 7870 km.
• The 1998 Return: The comet passed closest to the sun (1.034 AU) on 1998 November 21. The comet was rather faint at the beginning of summer, with a magnitude of 15 as June began, but steadily brightened. It surpassed magnitude 14 in late July, 13 just before mid-August, and then rapidly rose to magnitude 11 by the end of August. It then brightened at a rate of slightly less than one magnitude per month, reaching 10 by the end of September, 9 by the end of October, before peaking at magnitude 8.5 during the middle of November. Thereafter, as the comet moved away from both the sun and Earth, the brightness rapidly declined. It was fainter than 10 at the end of January, near 12 by the end of February, and was near 13 by the end of March.

External links:

• Cometography.com: Comet 21P/Giacobini-Zinner description.

Giacobini-Zinner missions: