Comet Ison
Comet Ison closing in on perihelion (Nasa)

Astronomers around the world will be waiting on tenterhooks to find out if Comet Ison, dubbed the Comet of the Century, will survive its close encounter with the sun after coming within 1.2 million miles of the solar surface in an event known as the perihelion.

The comet will either be torn apart by the sun, will use up all its ice and gas and fizzle out, or it will survive to pass behind the star and make it back towards Earth where it would be expected to be so bright that it would be visible during daytime.

Astronomers are hopeful that the comet could hold clues to how life on Earth originated.

Prof Mark Bailey, director of the Armagh Observatory in Northern Ireland, said it was unlikely that the comet would fizzle out during perihelion - the point at which it is closest to the solar surface - on Thursday (28 November).

"Its nucleus is of substantial size, some kilometres across, and whatever happens to it near perihelion - if it disintegrates or doesn't - a lot of the material will be released near the sun and that will become a very bright spectacle. Of course, being close to the sun we won't see it," he told IBTimes UK.

It is estimated that Ison is 2-3km wide but surviving would depend on its density.

"It's conceivable that the gravitational tidal force of the sun will split the nucleus into a small number of fragments," said Bailey.

"In that case they will move apart relatively slowly compared to the speed of the orbit around the sun. After perihelion distance, you will see the separate nuclei gradually drifting apart.

"The other alternative is that its body has some internal strength so it is not just held together by gravity but by the usual solid body forces. Then it will survive as an intact nucleus."

Comet Ison
Ison will reappear at the start of December if it survived (CometISON2013/Facebook)

Elizabeth Roche, astronomer at the Royal Observatory Greenwich, told IBTimes UK: "The size of it means that it is borderline between the ones that make it round and the ones that break up. Hopefully, it will be big enough to stay together and make it round the sun and look amazing on the other side, but you never know.

"It will be disappointing [if it doesn't make it round], but there are other comets. It's not our only chance of seeing a pretty awesome comet, it just could be a brilliant one because it's a sun-grazer, and you don't get that many of them."

Popular thinking suggests that Ison has come from the outer Oort cloud - the same source as the Great Comet of 1680 - although Bailey was doubtful.

"The outer Oort cloud is very thinly populated with comets. The chance of an object in the outer orb being scattered by the galactic tide or by a passing star into an orbit that is so close to the sun is relatively small.

Comet Ison
The comet may be broken up by the Sun (CometIson2013)

"It's coming from almost the same region and direction of the 1680/81 comet of Newton, and that's interesting because that was the comet that persuaded Netwon that comets orbit the ellipsis rather than moving in straight lines as Kepler believed.

"He thought initially it was two comets going in two straight lines. So that was a very important comet in terms of history and then there's this possibly coincidental link of Ison coming from the same direction."

Roche added that Ison could hold the keys to some of the secrets to the solar system.

"The comet is 4.6 billion years old so it was created when our solar system was created. It really is a relic from that time - a ball that is quite literally frozen in time.

"Being able to look at that shows us what our solar system was like 4.6 billion years ago.

"If you can look at the water in the comet, it will have a certain signature like a fingerprint, so you can identify that and if it matches the water we have on Earth, then that will add to the theory that a lot of the water on Earth came from comets and asteroids."

Should Ison survive its trip to the sun, it should be extremely bright in the sky and easily visible to the naked eye.

"It's going to produce a significant tail, and that tail will swing around the comet after perihelion so its advancing ahead of the comet," Bailey said.

"And we would hope that it will be a long straight tail visible in the morning sky in the first week or so of December, and after that in the evening sky as it moves farther north.

Comet Ison
The comet will never be seen again once it leaves the solar system (@NASA_GoddardPix) 

"I would suggest it will be as bright or a little brighter than Halley's Comet but not as bright as Comet Hale-Bopp. You will need a pair of binoculars to hand and look in the east and then increasingly in the northeast."

Roche said the comet has the potential to be "spectacular" and that it could be brighter than the Comet Ikeya-Seki from 1965.

"A lot of people are hoping we will see something like Comet Ikeya-Seki because that really was amazing.

"It's predicted it will be around the constellation of the Plough around Christmas Day. As we move into January it will come in the same region of our circumpolar constellations and will be up all night to see - hopefully. Obviously the better equipment you've got the better the image you'll get, so if you do have binoculars you can have a really good nose at it and with a telescope it will be even better again."

As for Ison's future, once it moves from our field of vision, it will never be seen again, Bailey said: "It seems to have a future orbit destined to leave the solar system. So whatever happens, this will by the last chance anyone on Earth has of seeing it.

"It's leaving on a hyperbolic orbit and will never come back."

Comet of the Century: Where to Watch Ison Before Close Encounter with Sun [PHOTOS]