Astronomer Robert G Harrington was the first to discover this comet during the National Geographic Society–Palomar Sky Survey. This comet was discovered on plates taken by a 122 cm Schmidt camera in August 1953.The comet was found in the constellation of Aquarius. As it was discovered by astronomer Harrington, the comet was named as Harrington.
Observations made about comet 51P/Harrington include:
- On its discovery apparition in 1953, the comet appeared diffused with a central condensation. It exhibited a tail less than one degree long.
- An image of this comet taken in 2001 apparition revealed that the comet had split into further two companions. The image showed two more nuclei.
On the discovery apparition in August 1953, the magnitude of comet 51P/Harrington was revealed at 15. The brightness was retained throughout September. This magnitude, however, dropped to 18 by October and by 10th December, it was 18.8. On its subsequent apparitions thereafter, the magnitude of comet 51P/Harrington was noted between 12.8–19.8. The magnitude of its two fragments was noted at about 21.3 and 20.2 respectively in 1994.
The perihelion distance (nearest to the sun) of comet 51P/Harrington was noted at 1.70 AU. Its aphelion distance (far from the sun) was noted at 5.73 AU.
The orbital period of comet 51P/Harrington was noted at 7.16 years. However, its orbital period changes due to perturbations caused by the gravitational effects of the giant planet Jupiter.
Comet 51P/ Harrington was recovered by astronomer Elizabeth Roemer (US Naval Observatory, Flagstaff Station, Arizona, USA). This comet was recovered in August 1960 3.45, which was also its perihelion date. The comet 51P/Harrington was next recovered in September 1980 by P. Jekabsons. However, its 1994 return was quite significant. According to a report by an IAU circular numbered 6089, astronomer Jim Scotti of Lunar and Planetary Observatory Arizona USA discovered that the comet 51P/Harrington had two companions with two separate nuclei. These were the fragments of the main nucleus of the comet.
Comet 51P/Harrington had a close encounter with the giant planet Jupiter on 19th November, 1920, 26th October, 1956 and on 23rd October, 2003.
The comet had last appeared on 12th August, 2015 and is next expected to appear around October 2022.