123P/West–Hartley

For other comets of the same name, see Comet West (disambiguation) and Comet Hartley.

Comet West–Hartley is a periodic comet with a 7.67-year orbit around the Sun.

123P/West–Hartley

Discovery image of Comet West–Hartley taken from ESO on 11 May 1989.[1]
Discovery
Discovered by	Richard M. West Malcolm Hartley
Discovery site	European Southern Observatory
Discovery date	11 May 1989
Designations
MPC designation	P/1989 E3, P/1995 S2
Alternative designations	1988 XVI, 1989k
Orbital characteristics[2][3]
Epoch	7 October 2026 (JD 2461320.5)
Observation arc	30.39 years
Number of observations	4,399
Aphelion	5.616 AU
Perihelion	2.159 AU
Semi-major axis	3.887 AU
Eccentricity	0.44469
Orbital period	7.665 years
Inclination	15.281°
Longitude of ascending node	45.848°
Argument of periapsis	103.88°
Mean anomaly	1.945°
Last perihelion	5 February 2019[4]
Next perihelion	21 September 2026[4]
TJupiter	2.832
Earth MOID	1.197 AU
Jupiter MOID	0.704 AU
Physical characteristics[2][5][6]
Mean radius	2.18±0.23 km
Synodic rotation period	3.7 hours
Comet total magnitude (M1)	8.2
Comet nuclear magnitude (M2)	13.8

Physical characteristics

The first attempts to measure the effective radius of its nucleus in 2000 were not successful due to too much scatter data in light curves obtained to provide reliable estimates.^[7] Recent attempts to measure the comet's light curves between 2004 and 2015 revealed that the nucleus is about 2.18 km (1.35 mi) in radius, rotating once every 3.7 hours.^[5]