Astronomer Henry L Giclas of Lowell Observatory, Arizona, USA was the first to discover this comet. The comet was discovered near the constellation of Cetus in September 1978. Astronomer Giclas also discovered a pre–discovery image of the comet from the plate exposed on September 3.33. The comet was named after its discoverer, Henry L Giclas.
Observations made about comet 84P/Giclas include:
- The comet appeared diffused and had no tail.
- It displayed condensation and a possible elongation towards the west.
- Astronomer Brian G Marsden published both, a parabolic and an elliptical orbit for the comet. The elliptical orbit was confirmed.
- The nucleus was estimated to be 1.8 km in diameter.
- Discovery apparition of the comet indicated a surge in the brightness due to its steady approach to the sun and earth.
- The comet started fading from October onwards and the observations were closed in March 1979.
On its discovery in the early September 1978, the magnitude of comet 84P/Giclas was noted at 15.6. In November the magnitude reached 17. After this, the comet appeared weak and diffused. In all its subsequent apparitions, comet 84P/Giclas revealed a magnitude of about 14–17.6.
The perihelion distance (nearest to the sun) of comet 84P/Giclas is noted at 1.852 AU while its aphelion distance (far from the sun) is noted at 5.443 AU.
Orbital period of comet 84P/Giclas is around 6.94 years.
Comet 84P/Giclas was recovered in June 1985 (estimated perihelion date). Astronomer Edgar Everhart of Chamberlin Observatory field station, Colorado, USA recovered it on an exposed plate obtained by John Briggs. An independent recovery made by C Y Shao of Oakridge Observatory on 18th July confirmed the earlier recovery. Astronomer Tsutomu Seki of Kochi observatory, Geisei station, Japan made a third independent recovery of the same comet on 22nd July. Astronomer Seki recovered this comet for the second time on 30th June, 1992 (expected perihelion date).
Comet 84P/Giclas did not have any close encounter with any planet apart from a close approach to the earth on 2nd October, 1978 at a distance of 0.81 AU.
The comet had last appeared on 23rd July, 2013 and is next expected to appear on 3rd June, 2020.