Comet ISON was discovered on Sept. 21, 2012, by astronomers Vitali Nevski and Artyom Novichonok of the International Scientific Optical Network. The abbreviation of the network is what the comet ISON is named after. Other astronomers had already reported a sighting of the comet. The two credited with the discovery used a 40 cm reflector telescope at Kislovodsk observatory in Russia. It was confirmed on Sept. 22, 2012, and announced to the world on Sept. 24, 2012, by the Minor Planet Center.
The International Astronomical Union name of the comet is C/2012 S1. The "C" means it is non periodic, or, in other words, will not orbit the Sun again for at least another 200 years. The "S" means it was discovered in the month of September.
The comet ISON has a parabolic orbit, which means it probably came from the Oort Cloud. The Oort Cloud is located approximately one light-year away. A light-year is 5.88 trillion miles or 9.46 trillion kilometers. The planet farthest from the Earth is 2.5 billion miles from the Earth, which is not nearly as far from Earth as the Oort Cloud.
As predicted, ISON was visible using small telescopes in Aug. 2013. ISON, like all comets, is composed of ice and dust. It comes closest to the Sun on Thanksgiving, which is Nov. 28. The speed that ISON travels varies, but at about 2:17 p.m., it is traveling at a speed of 217,170 miles per hour. It is in the constellation Libra and its visual magnitude is 2.01.
It is predicted the closest ISON will come to the Earth will be approximately 36 million miles from the Earth on Dec. 26 (the day after Christmas).
The size of the nucleus of ISON is estimated to be somewhere between 0.12 miles and three miles. This means ISON is expected to be about an average-size comet, although since this is the first encounter with ISON it is hard to estimate exactly how big the comet is. These predictions could be wrong, especially since most sungrazers only show up on an astronomer's radar a few hours before they come close to the Sun. However, the computer has increased the performance of radar observations.
ISON became visible without the aid of telescopes in November. It was located close to the star Spica in the constellation Virgo in the sky on Nov. 20, 2013. It is predicted it will not collide with the Sun during the close encounter on Thanksgiving Day November 28, but it might be destroyed (the behavior of a comet is not easy to predict). The distance it will be from the Sun is predicted to be about 730,000 miles, or 1.2 million kilometers.
A perihelion that close makes ISON qualify as a sungrazing comet. It might be dangerous if it explodes if it ends up hitting the Sun and sending its remains into the Earth. An asteroid hit Russia this year (2013) the same day that the asteroid 2012DA14 came within the Earth's atmosphere on February 15, so the predictions need to investigate the entire area where the object being studied is located.
ISON will come closest to the Earth the day after Christmas on Dec. 26, 2013. It is expected that the comet will be brightest to observers on the Earth on this day. Many have predicted it will be as bright as or as bright as the Moon. Around its closest approach on Thursday, Dec. 26, it might be bright enough to be seen in daylight.
When it was discovered, ISON was immediately anticipated to be the "Comet of The Century," but astronomers are not agreeing it will be so spectacular. The current Comet of The Century or, in other words, brightest comet this century, is Ikeya-Seki.
It might even be more brilliant than the Great Comet of 1680 (One of the greatest comets of modern times) according to some predictions. Often there is another comet a few hours before a spectacular comet. The Great Comet of 1843 has a period of 170 years, so it might be the "asteroid" that hit Russia Feb. 15, 2013, especially since it flew by the Earth in Feb. 1843. But comets are very unpredictable. It is also called the Great March Comet and its IAU name is C/1843 D1.
The path of the comet ISON will coincide with the Earth's orbit two times in 2014. This could be dangerous because the comet might leave big pieces of its tail. There will be a meteor shower both times, and it could be more brilliant than any meteor shower ever both times. The first time will be about Jan. 15 plus or minus a day or two. The second time will be about two weeks later.
The brightest comet this century (21st) is Comet McNaught (IAU C/2006 P1), which was seen in the southern hemisphere Jan. 2007. If comet ISON has a magnitude of -5.6, it will be brighter than comet McNaught. Some predict the comet will have a magnitude of anywhere from -11 to -16. This could be greater than the magnitude of the full Moon (-12.6). The Minor Planet Center thinks ISON could reach a magnitude of -9. Comet Ikeya-Seki reached a magnitude of -10 in 1966.
The controversial Great September Comet of 1882 could be the brightest comet that has ever been seen. It was claimed to have a magnitude of somewhere around -15 to -20! It came within about 264,000 miles at its closest approach to the Sun (perihelion). The day after, its nucleus broke into four pieces. It is not ISON, however, because its orbital period is 772+-3 years. Many of the other great comets have a similar orbital period.