They are one of the most spectacular views a human could hope to see and next year a comet that will outshine the moon is due to fly by the Earth.
Comet ISON is visiting the inner solar system and is set to put on spectacular views for the Northern Hemisphere across November and December next year as it heads towards the sun.
It may prove to be brighter than any comet of the last century, visible even in broad daylight, and this may end up being its one and only trip to the solar system, as its trajectory may see it plunge into the sun in a fiery death.
It is currently moving inwards from beyond Jupiter, and as it approaches the Earth, the â€œdirty snowballâ€ could produce a dazzling display, burning brighter than the moon and potentially being visible in broad daylight.
The comet, discovered by astronomers using the International Scientific Optical Network telescope in Russia, will pass within two million miles of the sun's surface making it s sun-grazing comet.
It is on a parabolic orbit, which means it probably originated from the outer skirts of the solar system, perhaps from the Oort cloud, a mass of icy debris which lies 50,000 times further from the sun than the Earth does.
If comet ISON survives the encounter, it could take thousands, potentially millions, of years before the comet passes back through the inner solar system.
The comet will begin brightening once it gets within Jupiter's orbit, as the sun's heat begins boiling the ice locked within the comet, converting it directly into gas.
It is likely to recall the excitement of Comet Hale-Bopp, which sailed past the Earth in 1997, appearing as a static-looking smear in the skies across the Northern Hemisphere.
It is also set to outshine the greatest comet of the last century Comet McNaught, which shone brighter than Venus as it passed above the southern hemisphere in 1965.
Comets are known as â€œdirty snowballs,â€ although technically a better definition would be snowy dirtballs, as comets are generally rocky at the surface, with chemical-laden ice within the interior.
As the ice and chemicals heat up, they erupt as brilliant jets which can form tails lasting hundreds of thousands of kilometers in length.
The comet is expected to be bright throughout late November and early December.
Robin Scagell, vice-president of the Society for Popular Astronomy, said: "This is a very exciting discovery. Our members will be eagerly following it as it makes its first trip around the Sun and hoping to see it shining brilliantly and displaying a magnificent tail as it releases powerful jets of gas and dust."
Source: Sky News