C/1975 T2 (Suzuki–Saigusa–Mori)
Long-period comet that became naked-eye visible and linked to a meteor shower.
C/1975 T2 (Suzuki–Saigusa–Mori) is a long-period comet that came within 0.104 AU of Earth on 31 October 1975, making it bright enough to see without a telescope. It was first spotted on 5 October 1975 by five observers in Japan, all within half an hour: Shigenori Suzuki, Yoshikazu Saigusa, Hiroaki Mori, Kiyomi Okazaki, and Shigeru Furuyama. The comet’s official name goes to the three discoverers whose telegrams reached the Central Bureau for Astronomical Telegrams first. Mori had already co-discovered another comet, C/1975 T1, 70 minutes earlier—the first time anyone found two comets in a single night. He used 20×120 binoculars; the others used reflector telescopes. Giovanni Casari in Italy also found it independently on 6 October. At discovery, the comet looked diffuse, with no central brightening or tail, and had an apparent magnitude of 9. It showed little motion because it was heading toward Earth. It brightened quickly after perihelion on 15 October, then moved toward Earth for its closest approach on 31 October. By 20 October its magnitude reached 8; John Bortle estimated it at 6.8 on 22 October and 5.5 on 28 October, when the coma had grown from 5 arcminutes on 12 October to 12 arcminutes. That same day, Bortle noted a tail about one degree long and a diffuse halo roughly one degree across. As the comet neared Earth, it passed between the Sun and our planet, reaching a solar elongation of just 5 degrees on 31 October. Its closest approach, at 0.104 AU, occurred at 14:43 UTC that day—one of the nearest observed comet approaches since 1930, matched only by C/1961 T1 (Seki). The comet then moved south and was recovered on 3 November. On 4 November, T. Morgan in Sydney estimated its magnitude at 4. David Seargent saw it with the naked eye on 6 November, putting its magnitude at 4.8. By 12 November it had faded to 7.2, and by 2 December to 9.5. It was last detected on 4 January 1976. The comet’s link to a meteor shower was proposed by Vladimir Guth and I. Hasegawa on 30 October 1975, as it neared its ascending node, but no definite activity was seen then. Between 2007 and 2011, cameras from the Croatian Meteor Network and SonotaCo detected meteors likely from this comet, now called the lambda Ursae Majorids, which peak on 28 October. Numerical models confirmed the connection.
Quick Facts
- Discovery Ref
- IAUC_2847
- Discoverer
- Shigenori Suzuki · Yoshikazu Saigusa · Hiroaki Mori
- Discovery Site
- Japan
- Discovery Date
- 5 October 1975
- Designations
- 1975 X, 1975kICQ1
- Orbit Ref
- jpldata
- Epoch
- 31 October 1975 (JD 2442716.5)
- Observation Arc
- 90 days
- Obs
- 112
- Aphelion
- 115.6 AU
- Perihelion
- 0.838 AU
- Semimajor
- 58.2 AU
Facts from the source article.
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, only the first three discoverers' names are appended to the comet. Mori had also co-discovered another comet, C/1975 T1 (Mori–Sato–Fujikawa), 70 minutes earlier, making him the first person to discover two comets in one night. Mori used 20×120 binoculars, while the other discoverers used reflector telescopes. The comet was also independently discovered 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 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 at 0.104 AU. This was, along with 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 magnitude 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 on 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, being one of the closest observed since 1930, and its association with a meteor shower. The possibility of a meteor shower was suggested by Vladimir Guth and I. Hasegawa on 30 October 1975 as the comet approached its ascending node, though no definite activity was observed at that time. Meteors potentially created by the comet were later detected by the Croatian Meteor Network and the SonotaCo from 2007 to 2011, and were named the lambda Ursae Majorids, which peak on 28 October. The link was confirmed with numerical models. The comet has also been suggested as the parent body of the October Ursae Majorids, first observed in 2006. Its discovery by five observers in a short span, and Mori's double discovery in one night, add to its historical interest.
Did You Know?
- Hiroaki Mori discovered two comets in one night, the first person to do so.
- The comet was discovered independently by five Japanese observers within 30 minutes.
- Its closest approach to Earth on 31 October 1975 was one of the closest observed since 1930.
- The comet is linked to the lambda Ursae Majorids meteor shower, which peaks on 28 October.
More in Named Comets, Part 3 1-24
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