ISON is a “sungrazer”, the type of comet that passes close to the sun as it enters the inner circle of the solar system. The comet’s actual name in the astronomical catalog is C/2012 S1 (ISON) but is generally shortened to ISON for the sake of convenience. The term ISON is an acronym that means International Scientific Optical Network, a Russian complex for astronomers.
It was here that Comet ISON was discovered by two Russian scientists, Vitali Nevski and Artyom Novichonok, using the telescope systems at ISON. The Russians confirmed their findings in the images returned to Earth by NASA’s Deep Impact Space Probe.
Deep Impact was a mission to Comet 9P/Tempel-1 that released a child ship which collided with that comet, then continued onwards. Deep Impact flew close by another comet, Hartley-2, and was used to observe still another comet called Garradd. The spacecraft is currently on course to fly close to a comet named (163249) 2002GT and is expected to reach that objective in 2020.
The Deep Impact mission confirmed for scientists that comets are composed of ice and dust as had been previously suspected. Comet ISON is no exception and is also composed of ice and dust. As a comet travels through space, it releases small particles of ice, dust and gas which trail out behind it, creating the characteristic tail for which comets are known. As a comet flies past the sun, the tail will point away from the sun because of the “solar wind” emitted by the sun.
As Comet ISON approaches Earth, it will grow significantly brighter, and many scientists believe it is possible that during the time the comet is visible from Earth, it could be brighter than the full moon. If this is the case then ISON would be visible to the naked eye in the night sky and could actually be quite a spectacular sight.
Comet ISON is believed by scientists to have originated in the Oort Cloud, which is a gigantic spherical cloud of icy objects at the edge of the solar system. The Oort Cloud extends outward from the solar system as far as one third of the distance to Alpha Centauri, the nearest star.
The perihelion is the closest point the comet will be to the sun. Comet ISON’s perihelion will be around 800,000 miles from the surface of the sun and will be reached on November 28. One month later, on December 26, the comet will reach its perigee or closest point to the Earth. Comet ISON’s perigee will be within 40 million miles of the Earth. Scientists say there is no danger of impact with the planet.
Comets throughout history have been seen as omens or signs of important events. Many ancient civilizations believed they foretold the death of a king. The Romans believed a comet foretold the death of Julius Caesar as he turned Rome from a Republic to an Empire. In 1066, Halley’s Comet was seen as a sign when William the Conqueror invaded England, executed Harold the Usurper and assumed his place on the throne.
Pope Calixtus III was written to have excommunicated Halley’s Comet in 1456. Halley’s Comet appeared in 1835, the year Mark Twain was born, and reappeared in 1910, the year he died. Twain himself said that he came in with Halley’s Comet and he would go out with it as well. The Black Death of 1347-1350 was accompanied by the appearance of a comet, and many at the time blamed the plague on this comet. The Inca believed that a comet foretold their 1533 conquest by Francisco Pizarro.
Scientists now know there are some comets that return relatively frequently, called short period comets. These are from a formation known as the Kuiper Belt and come in on the same orbital plane as the solar system. Others may only return after thousands of years and are called long period comets. These are comets from the Oort Cloud and they dive into the solar system from virtually any direction. Scientists believe this indicates the shape of the Oort Cloud is a sphere that encloses the solar system.