3 June 2020
Perihelion Distance (q)
Aphelion Distance (Q)
Click for NASA orbit diagram
Hills Observatory: 1 January 2013 to 26 May 2020
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.
17 Oct 13
29 Oct 13
9 Nov 13
14 Dec 13
26 Dec 13
5 Jan 14
25 Jan 14
5 Feb 14