C/1983 H1 (IRAS–Araki–Alcock)

Lore & Background

The comet was named after its discoverers – the Infrared Astronomical Satellite and two amateur astronomers, George Alcock of the United Kingdom and Genichi Araki of Japan. Both men were schoolteachers by profession, although Alcock was retired. Alcock had made his discovery simply by observing through the window of his home, using binoculars. During the closest approach, the comet appeared as a circular cloud about the size of the full moon, having no discernible tail, and shining at a naked eye magnitude of 3–4. It swept across the sky at an angular speed of about 30 degrees per day. On 11 May, the comet was detected on radar by Arecibo Observatory and Goldstone Solar System Radar, making it the first comet detected by two different radar systems. A second detection was made by Goldstone on 14 May. It is a long-period comet, with an orbital period of about 970 years, and is the parent comet of the minor Eta Lyrid meteor shower. This shower's radiant lies between Vega and Cygnus and produces 1 or 2 meteors an hour in mid-May with a peak between 9 May and 11 May. Comet IRAS–Araki–Alcock made its closest approach to Earth in 1983, at a distance of about 0.0312 AU. It was the closest approach up to that time of any comet in the last 200 years; only Lexell's Comet (1770) and 55P/Tempel–Tuttle (1366) are thought to have come closer.

Reader's Guide

Comet IRAS–Araki–Alcock holds significance as the closest known cometary approach to Earth in the 200 years prior to 1983, a record that underscores its rarity and the value of close-approach observations. Its discovery by both a space-based infrared satellite and two amateur astronomers—one of whom spotted it from his home window with binoculars—highlights the complementary roles of professional and citizen science. The comet's radar detection by two separate facilities (Arecibo and Goldstone) marked a first in cometary science, enabling comparative studies of its nucleus and coma. As the parent body of the minor Eta Lyrid meteor shower, it contributes a small but regular meteor display each May. The comet's legacy also includes contextualizing later close approaches, such as those of P/1999 J6 (SOHO) in 1999 and a fragment of 252P/LINEAR in 2016, which passed even nearer to Earth. Its brief, bright appearance as a moon-sized, tailless cloud moving rapidly across the sky remains a memorable event for observers.

Did You Know?

• Comet IRAS–Araki–Alcock was the first comet detected by two different radar systems (Arecibo and Goldstone).
• It made the closest known approach to Earth of any comet in the 200 years prior to 1983.
• One of its discoverers, George Alcock, spotted it using binoculars from his home window.
• The comet is the parent body of the minor Eta Lyrid meteor shower, which peaks between 9 May and 11 May.