Is the Comet Ison a Threat to the Earth

The comet Ison was discovered less than one year ago by Russian scientists Vitali Nevski from Vitebsk, Belarus and Artyom Novichonok from Kondopoga, Russia on September 21, 2012. It was named Ison after the initials of the International Scientific Optical Network. It was beyond the orbit of the planet Jupiter when it was first seen. Ison might come within 800,000 miles of the Sun on November 28, 2013. Comets that come close to the Sun are called sungrazers.

Ison might be as bright as the full moon when it is closest to Sun. Ison is also called C/2012 S1. In January it was in the constellation Gemini. It will be visible starting August 2013 to observers with a telescope or binoculars. Sometime in October it should be visible to the unaided eyes. The first of October  it will pass close to the star Regulus in the constellation Leo. Later in the month it will pass by the planet Mars.

In November it will pass the star Spica in the constellation Virgo. About the same time it will pass the planet Saturn in the sky. On November 28 at about 12:10 p.m. Pacific time it will come closest to the Sun at probably no farther than 1.1 million miles from it. This is equal to 1.8 kilometers or 0.012 astronomical units (AU). One AU is the distance from the Earth to the Sun. It is predicted that it might be as bright as the Moon or even visible in daylight. Another comparison is it will be ten times brighter than the planet Venus at -7 magnitude. This would make Ison the “comet of the century”.

Ison might not survive its close approach to the Sun. If it does not break up when closest to the Sun (perihelion), it will continue toward the Earth. It will be closest on the day after Christmas (December 26), when it will be about 39.6 million miles from the Earth. This distance is equal to 64 million kilometers or 0.34 AU. It will be in the constellation Draco at this time.tail was calculated at 40,000 miles long on March 10, 2013, but it might grow longer as it approaches the Sun.

Just over one hundred years ago on May 19, 1910 the Earth and the tail of Halley’s comet passed through each other. The comet had been visible starting on April 10, 1910 and reached its perihelion (closest to the Sun) on April 20, 1910. The distance to the Earth was 0.15 AU, or 13,950,000 miles.

A possible meteor shower has been predicted on about January 12, 2014 that will be caused by the tail of the comet ISON. Some of the debris might be big enough to make an impact on the Earth. The tail of the comet ISON will start increasing when it reaches the orbit of the planet Mars on about October 1. The solar wind from the Sun is strong enough to blow some of the coma into the tail at this point. This wind will be strongest when ISON is closest to the Sun on December 26 this year (2013). The solar wind could make the tail could grow to tens of millions of miles.

Comparing the possible tens of millions of miles of the tail of ISON to the 39.6 million miles closest approach on December 26 is an indication that the Earth will pass through the tail. It is predicted to possibly happen a few days before or after January 12, 2014. The tail of comets is mostly composed of dust and water. The hydrogen in the tail is known to be a threat of suffocation if it becomes too intense when the comet goes through the orbit of the Earth.