Last updated 09 Oct 2016

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Comet 112P/Urata-Niijima

Japanese astronomer Takeshi Urata discovered Comet 112P on images taken by Tsuneo Niijima on 1986 Oct 30th using a 0.30-m f/5.8 reflector, but reported it as asteroidal. It was given the minor planet designation 1986 UD and mentioned on IAUC 4267 as a fast moving asteroidal object. At that time it was moving at 2"/min in Aries, about 13' from the 11th magnitude galaxy NGC 772.

Tsutomu Seki observing four day later from Geisei noticed a "very faint and diffuse coma surrounding a central condensation" and the true cometary nature of the object was announced in IAUC 4269 on 1986 Nov 05, together with the new name Comet Urata-Niijima. Further observations, together with a pre-discovery position from 1986 Oct 29 and an independent discovery by Miklos Lovas from 1986 Nov 4th (IAUC 4270) allowed Brian Marsden at the Minor Planet Center to determine that the comet was in a short period orbit with P = 6.4 years. The apparition was very favourable, with the closest approach to Earth (0.48 AU) occurring three weeks before perihelion (1.449 AU) which was due on 1986 Nov 23.

A number of observatories followed the comet from 1986 November through to 1987 January, with the 0.9-m Spacewatch telescope at Kitt Peak recording the last images of it at the end of 1987 March as it receded from both Sun and Earth and approached conjunction with the Sun.

Six years later, IAUC 5882 announced the recovery of the comet by Jim Scotti at Kitt Peak with the 0.9-m Spacewatch telescope on 1993 Oct 20 & 21. Three months past an unfavourable perihelion passage in 1993 July, the comet was already 19th magnitude and fading fast as it pulled away from the Sun. The Spacewatch telescope was the only facility to report positions of the comet at this apparition with three further nights of observations, the last being 1994 Apr 6th.

The next perihelion passage was in 2000 March and this was even more unfavourable than 1993. The comet brightened on its way into perihelion at far southerly declinations but spent the majority of its time unobservable, very close to the Sun in the sky.
Photometry was obtained on 1999 July 14 with the 3.6-m NTT at La Silla when the comet was at a declination of -46, in an effort to determine the absolute nuclear magnitude, with the observed magnitude given as +21.3 and +21.4, but no astrometry appears to have been reported.
A single position of the comet taken on 1999 Sep 8 was made available by the Hubble Space Telescope, obtained during an exercise to determine the radius of the nucleus of selected comets.
Finally, three positions from the night of 1999 Nov 13 were reported from Kitt Peak.

The 2006 return was almost as favourable as the discovery apparition, with perihelion due on 2006 Oct 29 at a distance from the Sun of 1.47 AU and closest approach to Earth due two weeks later at a distance of 0.59 AU.

The comet was picked up from Great Shefford on 2006 Aug 2.1 UT in the early morning sky at magnitude +20.7 about 14" from the prediction. At that time it was 1.38 AU from Earth and 1.74 AU from the Sun. It was observed again very faintly on 2006 Aug 10.1 UT with a 45 minute exposure, despite the glare of the full moon some distance away low on the horizon. The comet appeared asteroidal on both occasions, without visible coma or tail.

The animation above was obtained during the next dark of the moon by which time the comet had brightened by about 1 magnitude. Confirmatory astrometry was obtained from the Schiaparelli Observatory in Italy by Luca Buzzi and Federica Luppi using a 0.60-m f/4.64 reflector on 2006 Aug 22.1 and 23.1 UT.


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