Comet ISON has been in the news for more than a year now. Discovered in September 2012, the comet should now be visible with binoculars or a small telescope.
ISON is a ‘sun grazer’ comet, as it will pass only 700,000 miles from the sun on November 28th. This distance is less than the sun’s diameter!
All comets primarily consist of dust and frozen compounds, such as carbon dioxide and water. As a comet approaches the Sun, the solar energy sublimates or vaporizes the frozen material. Gases and solids are pushed rapidly away from the comet by the solar wind, forming one or more tails. The solar wind is a stream of charged particles that races away from the sun.
A comet’s tail does not indicate the direction of the comet. In fact, the tail indicates the direction of the solar wind. Comets approach the sun with the tail trailing, but they move away from the sun with the tail first.
Depending upon several factors, there can actually be multiple tails. Comet McNaught in 2007 had at least 6 tails!
Comet ISON may not survive its close encounter with the Sun. However, if it does survive, the proximity of the Sun will likely vaporize enough of the frozen material to produce a significant tail.
Comet ISON will pass closest to Earth on December 26 at a distance of about 40 million miles.