123P/West-Hartley (0123P)

Type: Periodic Perihelion date: 5 February 2019 Perihelion distance (q): 2.1 Aphelion distance (Q) : 5.6 Period (years): 7.6 Eccentricity (e): 0.45 Inclination (i): 15.3 JPL orbit diagram COBS lightcurve Atlas Richard M. West (European Southern Observatory) discovered this comet on 11 May 1989 while examing plates exposed by G. Pizarro (La Silla) on 14 March for the ESO Quick Blue Survey extension. He described the comet as a condensation enveloped in a diffuse halo and noted a tail extending 0.5 arc minute toward PA 310°. Malcolm Hartley discovered a comet on a J survey plate exposed with the U. K. Schmidt on 28 May 1989 by S. M. Hughes. Marsden took the precise positions measured by West and Hartley and successfully linked them. They indicated the comet had passed perihelion on 1 October 1988. The perihelion distance was given as 2.42 AU and the orbital period was 6.61 years. Marsden considered the orbit was "still very uncertain." T. Gehrels and J. V. Scotti (Lunar and Planetary Laboratory, Arizona, USA) recovered the comet on 21 September 1995 with the 0.9-m Spacewatch telescope at Kitt Peak. The total magnitude was estimated as between 18.8 and 19.1, the magnitude of the nuclear condensation was 21.1. Close approaches to planets: • 0.79 AU from Jupiter on 25 December 1939 (decreased perihelion distance from 2.33 AU to 2.23 AU and decreased orbital period from 8.29 to 7.95 years) • 0.68 AU from Jupiter on 21 September 1963 (decreased perihelion distance from 2.23 AU to 2.18 AU and decreased orbital period from 7.94 to 7.71 years) Observations (VEMag = visual equivalent magnitude) Date 10x10 mag Error VEmag Coma ' 12-Oct-18 17.22 0.24 16.8 0.2 04-Dec-18 16.26 0.03 15.1 0.6 11-Dec-18 16.11 0.01 15.0 0.7 18-Dec-18 15.92 0.02 14.8 0.6 02-Jan-19 15.55 0.02 14.1 0.8 09-Jan-19 14.88 0.01 13.6 0.6 16-Jan-19 14.29 0.01 12.8 0.7 07-May-19 15.75 0.02 12.7 1.2 27-May-19 16.23 0.06 13.1 1.3