| C/1993 Y1 (McNaught–Russell) | |
| Discoverer: | Robert H. McNaught Kenneth S. Russell |
| Discovery Site: | Siding Spring Observatory |
| Discovery Date: | 17 December 1993 |
| Mpc Name: | C/1993 Y1 C/574 G1 |
| Designations: | 1994 XI 1993v |
| Epoch: | 28 April 1994 (JD 2449470.5) |
| Observation Arc: | 265 days |
| Obs: | 377 |
| Perihelion: | 0.8676 AU |
| Aphelion: | 270 AU (inbound) 240 AU (outbound) |
| Eccentricity: | 0.9932 |
| Period: | 1,600 years (inbound) 1,300 years (outbound) 1,430 ± 30 a |
| Inclination: | 51.586° |
| Asc Node: | 166.359° |
| Arg Peri: | 353.468° |
| Tjup: | 0.755 |
| Earth Moid: | 0.1212 AU |
| Jupiter Moid: | 2.6212 AU |
| Magnitude: | 6.5 (1994 apparition) |
| M1: | 12.3 |
| M2: | 16.9 |
| Last P: | 31 March 1994 |
| Next P: | ~3300 |
Comet McNaught–Russell, formally designated as C/1993 Y1, is a long-period comet that reached a maximum magnitude of 6.5 (just below naked eye level) in early 1994. It was discovered by Robert H. McNaught and Kenneth S. Russell using the U.K. Schmidt Telescope in Australia. McNaught and Russell worked at Siding Spring Observatory and together discovered five comets between 1991 and 1995.
Its orbital period was found to be very high – initially estimated at over 1400 years.
| C/574 G1 | |
| Discovery Site: | China |
| Discovery Date: | 4 April 574 |
| Epoch: | 25 March 574 (JD 1930794.5) |
| Observation Arc: | 49 days |
| Obs: | 3 |
| Period: | 1,430 ± 30 years |
| Perihelion: | 0.730 AU |
| Inclination: | 54° |
| Asc Node: | 155° |
| Arg Peri: | 342° |
| Last P: | 25 March 574 31 March 1994 |
| Next P: | ~3300 |
It was noted by Francois Colas (Paris observatory) and Ichiro Hasegawa that the path of McNaught–Russell coincided with that of comet C/574 G1, which was recorded in AD 574 over a period from April 4 to May 23 by observers in China. This would give the comet a period of 1430 ± 30 years and so making it the longest period comet to be seen on two separate returns. Since the comet was not observed to approach any planets, its orbit should remain largely unchanged on its next return. This would place its next approach to the inner Solar System around 3300.