84P/Giclas (0084P)


Type: Periodic Perihelion date: 3 June 2020 Perihelion distance (q): 1.7 Aphelion distance (Q) : 5.4 Period (years): 6.7 Eccentricity (e): 0.52 Inclination (i): 7.6 JPL orbit diagram COBS lightcurve Henry L. Giclas (Lowell Observatory, Arizona, USA) discovered this comet in Cetus on 8 September 1978. He determined the magnitude as 15.6, and described it as diffuse, with a condensation and a possible elongation toward the west. Giclas subsequently found a prediscovery image on a plate exposed on 3 September. Using positions obtained through 12 September 1978, Brian G. Marsden published both a parabolic and an elliptical orbit on 14 September. The parabola indicated a perihelion date in January 1979, while the elliptical orbit indicated perihelion would occur in November 1978. The latter orbit also indicated an orbital period of 6.74 years. Marsden commented, "The elliptical elements seem more probable" though he noted the eccentricity, and therefore the orbital period, was uncertain. A few days later the elliptical orbit was confirmed and on 18 September Marsden published an orbit with an orbital period of 7.16 years. The orbit was continually revised during the comet's entire apparition, although Marsden's orbit published on 2 October was the first to very closely match the comet's final orbit. It indicated a perihelion date of 21 November 1978 and an orbital period of 6.68 years. Observations obtained during the comet's discovery apparition indicated a possible brightening following discovery as several observers gave the magnitude as 15 to 15.2 during the remainder of September. This was no doubt a result of the comet's steady approach to both the sun and Earth. The comet passed closest to Earth on 2 October 1978 (0.81 AU) and a slow fading seem to set in thereafter. By mid-October the magnitude was estimated as near 15.5, and it was close to 16 by the end of the month. The comet passed closest to the sun on 21 November (1.73 AU) and by the end of the year the brightness was given as 17.0. Observations finally ended on 28 March, when astronomers at Harvard College Observatory's Agassiz station described the comet as weak and diffuse. The comet was next predicted to return to perihelion in 1985. Edgar Everhart (Chamberlin Observatory field station, Colorado, USA) recovered the comet on an exposure obtained by John Briggs with the 0.4-m reflector on 22 June 1985. The recovery went unconfirmed until an independent recovery was made by C. Y. Shao (Oak Ridge Observatory) on an exposure obtained by G. Schwartz on 18 July. Everhart estimated the brightness as magnitude 20, while Shao estimated it as 18. A third independent recovery was made by Tsutomu Seki (Kochi Observatory, Geisei station, Japan) on 22 July. He estimated the magnitude as 18.5. The precise positions indicated the prediction by S. Nakano required a correction of -0.66 day. Shao and Seki both noted the comet was so condensed it was nearly stellar in appearance. Although the comet was predicted to become no brighter than magnitude 16, amateur astronomers found it slightly brighter than magnitude 13.5 during the latter half of October. By December the brightness had dropped to 14 and the comet was last detected on 19 January 1986, when T. Gehrels and James V. Scotti determined the magnitude as 16.9. The comet was next expected at perihelion in 1992 and Seki recovered it on 30 June 1992. He estimated the magnitude as 18 and described the comet as diffuse with a central condensation. The comet brightened and slightly surpassed 15th magnitude during November and December. It was last seen on 20 March at magnitude 17.6. During 1995 Brian Skiff (Lowell Observatory, Arizona, USA) began measuring the positions of minor planets on plates taken by Clyde W. Tombaugh (Lowell Observatory) during the 1930's. On plates exposed on 12, 16 and 21 September 1931 Skiff found images of a comet. Precise positions were measured and Skiff sent the information to B. G. Marsden of the Central Bureau for Astronomical Telegrams. Marsden tried to fit an orbit to the positions and found an elliptical one represented the observations best. The positions and orbit were published in April 1995. Observations (VEMag = visual equivalent magnitude) Date 10x10 mag Error VEmag Coma ' 17-Oct-13 17.22 0.12 16.9 0.2 29-Oct-13 16.97 0.07 16.7 0.2 09-Nov-13 16.98 0.03 16.7 0.2 14-Dec-13 16.58 0.15 15.4 0.3 26-Dec-13 16.39 0.03 15.5 0.4 05-Jan-14 16.87 0.03 16.0 0.4 25-Jan-14 17.65 0.05 16.3 0.3 05-Feb-14 18.16 0.07 17.8 0.3 18-Sep-20 17.16 0.07 16.6 0.4 26-Oct-20 16.9 0.4 13-Nov-20 17.5 0.4