Comet C/2012 S1 (ISON)

Formal discovery announced on CBET 3238 of the International Astronomical Union's Central Bureau for Astronomical Telegrams (which included part of the text below).

Vitali Nevski (Vitebsk, Belarus) and Artyom Novichonok (Kondopoga, Russia) reported their discovery of a diffuse comet with an 8" coma on four 100-s CCD exposures obtained on Sept. 21.06 UT with a 0.4-m f/3 Santel reflector of the International Scientific Optical Network (ISON) near Kislovodsk, Russia. Nevski and Novichonok first reported the object to the Minor Planet Center (MPC) with no mention of cometary appearance, and it was posted on the MPC's NEOCP webpage as an apparently asteroidal object (their report to the Central Bureau for Astronomical Telegrams about cometary appearance arrived nearly a day after NEOCP posting); this resulted in the comet being named "ISON" by the Central Bureau, as per the IAU comet-naming guidelines.

Follow-up observations obtained with a 1.5-m f/8 reflector at the Majdanak observatory in Uzbekistan by O. Burhonov (measured by Novichonok and Nevski) on Sept. 21.99 UT showed an obvious elongation in p.a. 305 deg with a coma of size 9" x 11" and total mag about 17.1. After the object was posted on the MPC's NEOCP webpage, other CCD astrometrists commented on the object's cometary appearance (including one or two such reports received before Nevski's e-mail to the Central Bureau noting cometary appearance). W. H. Ryan (Magdalena Ridge Observatory, 2.4-m f/8.9 reflector) noted an elongated nuclear condensation and a faint tail in p.a. about 280 deg on R-band images taken on Sept. 21.4; follow-up images taken by W. H. Ryan and E. V. Ryan on Sept. 22.4 and 23.4 show an elongated nuclear condensation and a distinct tail in p.a. about 280 deg. H. Sato (Tokyo, Japan; remotely using a 0.51-m f/6.8 astrograph at the RAS Observatory near Mayhill, NM, U.S.A., on Sept. 22.5) found a disk-like object 10" in diameter. E. Guido, G. Sostero, and N. Howes stacked twenty-four 120-s unfiltered exposures obtained remotely on Sept. 22.5 with a 0.25-m f/3.4 reflector at the RAS Observatory near Mayhill to find a slightly diffuse object that was slightly larger than nearby field stars of similar brightness.