C/2012 S1 (ISON) is a sungrazing comet discovered on 21 September 2012 by Vitali Nevski (Виталий Невский, Vitebsk, Belarus) and Artyom Novichonok (Артём Новиночок, Kondopoga, Russia). The discovery was made using the 0.4-metre (16 in) reflector of the International Scientific Optical Network near Kislovodsk, Russia. Precovery images by the Mount Lemmon Survey from 28 December 2011 and by Pan-STARRS from 28 January 2012 were quickly located. Follow-up observations were made on 22 September by a team from Remanzacco Observatory in Italy using the iTelescope network. The discovery was announced by the Minor Planet Center on 24 September, three days after the discovery.
The preliminary orbit shows the comet will come to perihelion (closest approach to the Sun) on 28 November 2013 at a distance of 0.012 AU (1,800,000 km; 1,100,000 mi) from the center point of the Sun. Accounting for the solar radius of 6.955×105 km, the comet will pass approximately 1,100,000 kilometres (680,000 mi) above the Sun’s surface. Its orbit is nearly parabolic, which suggests that it may be a new comet coming fresh from the Oort cloud. Preliminary calculations show that, on closest approach, the comet will pass about 0.07 AU (10,000,000 km; 6,500,000 mi) from Mars on 1 October 2013, and it will pass about 0.4 AU (60,000,000 km; 37,000,000 mi) from Earth on 26 December 2013.
At the time of its discovery, the comet’s apparent magnitude was about 18.8, far too dim to be seen with the naked eye but bright enough to be imaged by amateurs with large telescopes. It will gradually increase in brightness as it approaches. Around August 2013 it should be visible through small telescopes or binoculars, becoming visible to the naked eye by late October or early November and remaining so until mid-January 2014. When the comet reaches its perihelion on 28 November it may be less than 1° from the Sun, making it difficult to see against the glare of the Sun.[ The comet may become extremely bright if it remains intact, probably reaching a negative magnitude. According to Astronomy Now, it may briefly become brighter than the full Moon. But predicting the brightness of a comet is difficult, especially one that will pass so close to the Sun and be affected by the forward scattering of light. Comet Kohoutek and C/1999 S4 did not meet expectations, but if ISON survives it could look similar to the Great Comet of 2007, the Great Comet of 1680 or C/2011 W3 (Lovejoy The brightest comet since 1935 was Comet Ikeya–Seki in 1965 at magnitude -10. Comet ISON will be well placed for northern hemisphere observers in mid to late December 2013
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Astronomical centre staff will monitoring the comet.