C/1975 T2 (Suzuki–Saigusa–Mori)

Lore & Background

The comet was discovered independently on 5 October 1975 by five Japanese observers within 30 minutes: Shigenori Suzuki, Yoshikazu Saigusa, Hiroaki Mori, Kiyomi Okazaki, and Shigeru Furuyama. By international agreement, the comet bears the names of the three discoverers whose telegrams arrived first at the Central Bureau for Astronomical Telegrams, hence Suzuki–Saigusa–Mori. Mori had also co-discovered another comet, C/1975 T1 (Mori–Sato–Fujikawa), 70 minutes earlier, marking the first time a person discovered two comets in one night. Mori used 20×120 binoculars, while the other discoverers used reflector telescopes. The comet was also discovered independently by Giovanni Casari on 6 October. Upon discovery, the comet was described as diffuse, without central concentration or tail, with an apparent magnitude of 9. It displayed very little apparent motion as it was heading toward Earth. The comet brightened rapidly after perihelion on 15 October and moved toward Earth, with closest approach on 31 October. On 20 October its magnitude was 8; on 22 October John Bortle estimated magnitude 6.8; on 28 October he estimated magnitude 5.5, with the coma increasing from 5 arcminutes on 12 October to 12 arcminutes on 28 October. On 28 October Bortle also reported a tail about one degree long and a diffuse halo about one degree across. On 31 October the comet was at a solar elongation of 5 degrees and made its closest approach to Earth at 0.104 AU. This was, along with the equally close approach of C/1961 T1 (Seki), the closest observed approach of a comet to Earth since 1930. The comet moved southward and was recovered on 3 November. On 4 November T. Morgan estimated its magnitude at 4. On 6 November David Seargent spotted it with the naked eye at magnitude 4.8. By 12 November it had faded to magnitude 7.2, and by 2 December to 9.5. The comet was last detected on 4 January 1976.

Reader's Guide

The comet's significance lies in its close approach to Earth—0.104 AU on 31 October 1975—which, along with C/1961 T1 (Seki), was the closest observed approach of a comet to Earth since 1930. This proximity allowed it to become visible to the naked eye, with magnitude estimates as bright as 4. The comet's rapid brightening and large coma (12 arcminutes by 28 October) and tail (about one degree) made it a notable object for amateur observers. Its association with the lambda Ursae Majorids meteor shower, confirmed by numerical models and detected by the Croatian Meteor Network and SonotaCo from 2007 to 2011, adds to its legacy. The shower peaks on 28 October. The comet has also been suggested as the parent body of the October Ursae Majorids, first observed in 2006. The discovery story is remarkable: five Japanese observers independently found it within 30 minutes, and one of them, Hiroaki Mori, had discovered another comet earlier the same night—the first time a person discovered two comets in one night.

Did You Know?

• The comet was discovered by five Japanese observers within 30 minutes on 5 October 1975.
• Hiroaki Mori discovered two comets in one night, the first person to do so.
• The comet's closest approach to Earth was 0.104 AU on 31 October 1975, the closest since 1930 (along with C/1961 T1).
• The comet is associated with the lambda Ursae Majorids meteor shower, which peaks on 28 October.