C/1963 F1 (Alcock)

Lore & Background

George Alcock discovered the comet using his 25 × 105 binoculars on the morning of 19 March 1963. At that time it was a diffuse 8th-magnitude object with a short tail about 2° northwest of the star δ Cyg. Subsequent observations included a photographic session from the Flagstaff Observatory, and by the end of April the comet had steadily brightened to 7.5 in apparent magnitude.

The comet reached perihelion on 5 May and made its closest approach to Earth about four days later. Its brightness initially remained slightly lower than predicted by its ephemerides, until an outburst on 30 May raised its peak magnitude from 5.8 to 4.4. The nucleus was then observed to split into two, and later five pieces on 23 June, following several subsequent outbursts that began about a week earlier. By 19 July, John C. Bennett reported the comet had faded to a 9th-magnitude object with a slightly elongated coma. It was last observed in August 1963.

During the outbursts, significant amounts of CN, C2 and C3 were detected, and an estimated 2.19×10⁸ kg of dust was ejected into space.

Reader's Guide

C/1963 F1 (Alcock) is significant as the third of five comets discovered by English astronomer George Alcock, a prolific visual comet hunter. Its series of outbursts, which caused the nucleus to split into as many as five pieces, provided a rare opportunity to study the fragmentation and chemical composition of a comet in real time. The detection of CN, C2 and C3 during these events, along with the ejection of over 200 million kilograms of dust, offered insights into the volatile and dust content of cometary nuclei. The comet's brightness fluctuations, including a peak magnitude of 4.4 that made it barely visible to the naked eye, and its deviation from predicted ephemerides, highlight the unpredictable nature of cometary activity. Its legacy lies in the detailed observational record of its outbursts and fragmentation, which contributed to the understanding of cometary behavior and the processes that drive sudden brightening and disintegration.

Did You Know?

• The comet was discovered using 25 × 105 binoculars.
• Its nucleus split into two, then five pieces on 23 June 1963.
• During outbursts, CN, C2 and C3 were detected, and 2.19×10⁸ kg of dust was ejected.
• It is the third of five comets discovered by George Alcock.