IT IS being billed as the "comet of the century" and could be the most spectacular sky event in 100 years or a big fizzer.
Comet Ison, making its first visit to the inner Solar System, will pass Earth early on Tuesday morning as it makes its way around the Sun.
Australian astronomer Dave Reneke said the best time to look for Ison was about an hour and a half before sunrise and a bit to the right of the planet Mars
Mr Reneke said like all comets, Ison was a big ball of frozen gases and water mixed with rock and dust.
This ball, the comet's nucleus, appears to be about 4km wide, large as comets go.
As Ison approaches the Sun, the heat vaporises some of the comet's surface.
The Sun pushes some of this material outward to form a glowing tail kilometres or more long.
Some are speculating the comet may break up from the gravity of the Sun.