We have a relatively bright comet (relative to most comets viewable to us) in our skies currently. Comet PANNStars has been giving most of the Earth a little bit of a show just after sunset. Later this year we may be treated to an incredible sight as comet ISON threatens to be as bright as, if not brighter than, our moon.
Comets are chunks of ice and rock that orbit our sun. Many come from the Oort Cloud located beyond Pluto. As they reach the inner solar system and approach the sun, the ice starts to melt and the gases react with the sun’s solar wind and creates 2 tails, one of gas and one of dust, which extend behind the comet away from the sun.
The comets out there take anywhere up to 30 million years to orbit the sun one time, which is why most comets we see are once in a lifetime for us. So whenever there’s a good one out there, you’re going to want to take the opportunity to get a good look at it!
More info about comets can be found HERE.