comets

[fiona_]

ello... i know that recently there's two comets that can be seen .... but actually im not very sure of how u would define as comet cuz from what i have been readin from this forum it appears that the comet can be seen for a few days which i conclude that its like a star and stays in a same place unlike a meteor that disappears within seconds..

[Airconvent]

ello... i know that recently there's two comets that can be seen .... but actually im not very sure of how u would define as comet cuz from what i have been readin from this forum it appears that the comet can be seen for a few days which i conclude that its like a star and stays in a same place unlike a meteor that disappears within seconds..

hi fiona,
comets are typically objects left over from the creation of our solar system. they are mainly fragments of rock and ice with sizes ranging from miniscule up to Pluto-sized. They generally lurk in an area near the edge of our Sun's influence called the Oort cloud. Sometimes, passing stars , etc can pull some of these objects towards our sun. They usually approach our sun, do a loop and then move out as governed by the law of gravity.
some comets get locked in a close orbit, with cycle times of 3-4 years while some such as Halley's comet takes about 70+ years. Unless I am mistaken, the current 2 takes tens of thousands of years to orbit the sun, so we won't be seeing them again in our lifetime after this.
as this objects approach the sun, the sun heats up their surface and the ice evaporates. the solar wind then pushes it backwards forming a tail. How long and bright the tail will depend on the composition of that comet as well as how many times it has approached the sun. Older comets have most of their ice blasted away by solar wind, so do not have any tail.
comets can be see for months as they approach , loop around the sun and then leave. the only difference is their brightness. further away from the sun, they would be dim.

do not get mixed up with meteors which are dust and fragments that enter our atmosphere and gets burned up in a few seconds.

rich

[fiona_]

so does that mean we won't be able to see it in motion , with only the increasing brightness indicating its movement ? Im confused !!!! I mean , i've seen pics of hale-bopp and haley's comet and they look everything but stationary . u know , like a much larger meteor that just shoots across and diappears.

[chrisyeo]

Fiona, the observed motion is because of the comet's tail, but the tail is not because it is speeding across the sky. It is actually a cloud of dust behind the comet.

Cheers

[zong]

comets can be see for months as they approach , loop around the sun and then leave. the only difference is their brightness. further away from the sun, they would be dim.

Actually, at a certain distance away from the sun, no matter if it's approaching or heading away from the sun, it will not be bright any more. This is because the level of solar wind activity is not high enough to cause any more "burning" of the comet, much less create a tail. Therefore to say they are dim is not totally true because they are not dim, they're totally invisible even with our telescopes (again, only in Singapore's case..)

Fiona, it doesn't mean we can't see the comet move, if it is visible to the naked eye then we can actually see it "move" with respect to the background stars, as it moves relatively faster than the background stars "move" in our sky. The increase in brightness shows that it is getting nearer to the sun, as there will be a higher level of solar wind activity.

[fiona_]

well thanks for the replies .. i've got a faint idea of what to expect already but still i'm kinda confused. Chrisyeo said that 'Fiona, the observed motion is because of the comet's tail, but the tail is not because it is speeding across the sky. It is actually a cloud of dust behind the comet.'. So , does that mean that the photos of famous comets like hale-bopp , like this one in this picture from are actually not what they seem to be , which is in very fast motion spanning only a few seconds ( thats what the tail indicates to me ) . Oh dear , i hope im not confusing u guys with my rookie questions. By the way , u guys organising any comet watching sessions ?

'

[Airconvent]

The comets are actually moving very fast by human standards (a whole lot faster than a Porche 911!) but they don't seem to move when observed from earth as they are quite far away. On a scope at high mag, it may be possible to see it change position slightly over a period of time.

Also, most people have the misconception that the comets tail is "behind" the comet. In reality, it should be pointing away from the sun regardless of where it is since the tail is caused by solar wind beating on the comet's nucleus.
Hence for the pic you attached, I know the sun is generally at bottom left of the picture but the comet could be moving towards top right and the tail will still be where it is shown.

rich

[fiona_]

yes , i know that the tails shld point away from the sun and the solar wind stuff but it still confuses me to think how the tail looks like its in fast perpetual motion.. lol... And also... the halebopp pic i attached in my previous reply looks so HUGE , almost like the sun !! So in 1997 the skies were actually so illuminated by it ? So did any1 of longtime astronomer managed to catch it way back in 97 or did light pollution here caused some probs as usual ?

[Airconvent]

yes , i know that the tails shld point away from the sun and the solar wind stuff but it still confuses me to think how the tail looks like its in fast perpetual motion.. lol... And also... the halebopp pic i attached in my previous reply looks so HUGE , almost like the sun !! So in 1997 the skies were actually so illuminated by it ? So did any1 of longtime astronomer managed to catch it way back in 97 or did light pollution here caused some probs as usual ?

whether it looks huge is relative. I think its fairly bright but as to its size, a good magnification on the scope would be able to achieve that effect.

rich

[fiona_]

Okay.. So how about the two visible comets now ? apparently even with a telescope here in Sg the tail cant be seen , judgin from photos seen