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View Full Version : Our old friend Haleys comet...!!



Hazzard
2005-Mar-31, 10:03 AM
It shows up every 76th year....goes around our sun then takes of again.

But here is what i dont know..

Were is THE OTHER turning point,that sends Haley back to us everytime.

Iv looked everywere but came up with nothing.
So I came to the conclusion that we just dont know...am I right?? 8-[

jt-3d
2005-Mar-31, 10:13 AM
Of course we do. First google hit (http://csep10.phys.utk.edu/astr161/lect/comets/halley.html).

Edit: Apparantly there is some wiggle room though. It's not a consistant period so I guess has to be recalculated after each orbit to account for the influence of Jupiter and Saturn. I did not know this. #-o

Hazzard
2005-Mar-31, 10:30 AM
But that doesnt realy make any sense to me..!!??? :cry:

Does this meen that its our sun that pulls it back towards us.

Or is the comet turning around some other celestial bodys gravityfield, beyond Pluto??

Kullat Nunu
2005-Mar-31, 11:26 AM
But that doesnt realy make any sense to me..!!??? :cry:

Don't panic. ;)


Does this meen that its our sun that pulls it back towards us.

Yes, it means exactly that. Actually Sun pulls it constantly.

You can think following experiment: You have a very large rubber sheet ("space") and a massive ball ("Sun") in the center of it. The ball causes a depression on the sheet ("Sun's gravity well"). Now, you put a small marble (comet, planet, asteroid) on the sheet and very slightly nudge it. The marble starts to fall into the depression (Sun's gravity well), but if you didn't nudge it directly towards the heavy ball it won't collide it. Instead it passes it and climbs back up on the rim of the depression. (We exclude friction here.) If you nudged the ball too much it could climb too fast and leave the depression altogether. Otherwise it keeps falling and climbing indefinitely i.e. it's in the orbit around the heavy ball.


Or is the comet turning around some other celestial bodys gravityfield, beyond Pluto??

No, and it won't go that far. It slows until it no longer moves further and starts to "drop" back towards the Sun. Fortunately for it, the comet has some tangential velocity to keep it in an elliptical orbit, otherwise it would fall directly into the Sun.

If it gets enough energy (for example making a very close flyby of Jupiter) it can escape from the Solar System. Some comets have done that.

Hopefully I didn't confuse you even more. :)

worzel
2005-Mar-31, 12:14 PM
Of course we do. First google hit (http://csep10.phys.utk.edu/astr161/lect/comets/halley.html).
Isn't the tail pointing the wrong way in those diagrams? I thought the tail always pointed away from the sun.

Hazzard
2005-Mar-31, 12:18 PM
To Kullat Nunu....




Quite the opposite my friend :P

That makes perfect sence,thanks alot.

Nicolas
2005-Mar-31, 12:19 PM
Of course we do. First google hit (http://csep10.phys.utk.edu/astr161/lect/comets/halley.html).
Isn't the tail pointing the wrong way in those diagrams? I thought the tail always pointed away from the sun.

I thought this too? Any clarification?

Hazzard
2005-Mar-31, 12:24 PM
Of course we do. First google hit (http://csep10.phys.utk.edu/astr161/lect/comets/halley.html).
Isn't the tail pointing the wrong way in those diagrams? I thought the tail always pointed away from the sun.

I thought this too? Any clarification?

Its only a diagram. :)

And too far out , I doubt the solarwind effects the comet that much to create its tail.

Nicolas
2005-Mar-31, 12:27 PM
Of course we do. First google hit (http://csep10.phys.utk.edu/astr161/lect/comets/halley.html).
Isn't the tail pointing the wrong way in those diagrams? I thought the tail always pointed away from the sun.

I thought this too? Any clarification?

Its only a diagram. :)
And that far out the I doubt the solarwind effects the comet that much to create its tail.

I thought the discussion here said that the tail wasn't always pointing away from the sun, hence my confusion.

So my memory was correct that the tail always points away from the sun. (unless in an environment where other forces become dominant, like in some dust cloud environments...). Far away from the sun, there will be little to no tail indeed.

Argos
2005-Mar-31, 12:59 PM
Or is the comet turning around some other celestial bodys gravityfield, beyond Pluto??

No, and it won't go that far. It slows until it no longer moves further and starts to "drop" back towards the Sun.

Yeah. As a matter of fact, Halley comet wonīt even get to halfway between the Sun and Pluto in its aphelion.

Hazzard
2005-Mar-31, 01:39 PM
Thats NOT what the diagram shows.

To me it looks as if its out there by Pluto somewere.

Kullat Nunu
2005-Mar-31, 02:23 PM
The tail is badly wrong in the diagram, but I suppose it wasn't meant to be right.

First, the ion tail of the comet points always away from the Sun, as the lightweight ions are carried by the solar wind.
Secondly, the dust tail, which constist of heavier dust, isn't as much affected by the solar wind as the ion tail, so it has somewhat curved shape. It's the dust tail which is usually best visible.
And finally, the comet has its tail only when it is close to the star. Actually, somewhere at the distance of Jupiter the coma and the tail starts to form (I'm not sure about this and it depends of the comet, of course). Mostly the comet is just a frozen ball of ice and dirt. So seeing Halley now is quite a challenge, but ESO astronomers have succeeded doing so (http://www.eso.org/outreach/press-rel/pr-2003/phot-27-03.html). This means that Halley is now visible through its orbit.

Romanus
2005-Mar-31, 05:01 PM
For complete neophytes:

One can easily calculate the periapsis and apoapsis of any orbiting body with the following formulae:

periapsis = (1 - e)a
apoapsis = (1 + e)a

a = semimajor axis (avg. distance from sun / planet / etc.)
e = eccentricity (from 0 to < 1)

So for Halley's comet, where a = 17.8 AUs, and e = .967, perihelion is:

(1 - .967)17.8 = .587 AUs (well inside the orbit of Venus)

--and aphelion is:

(1 + .967)17.8 = 35 AUs

Also, keep in mind that Halley's orbit is steeply inclined from the plane of the ecliptic; it doesn't really come close to any major planets besides Earth and Venus. The site below gives an excellent representation of its orbit:

http://neo.jpl.nasa.gov/cgi-bin/db_shm?sstr=Halley&group=com&search=Search

erisi236
2005-Mar-31, 05:09 PM
Where is it right now as we speak anyway? How far away from Earth? :-k

Argos
2005-Mar-31, 10:00 PM
Thats NOT what the diagram shows.

To me it looks as if its out there by Pluto somewere.

I must apologize, cause you are right. For a moment the scale of the orbits escaped me. It goes a little further than Neptuneīs orbit (I had Uranus in mind - shame on me). In fact itīll be as far as Pluto (in terms of absolute distance from Earth) in its aphelion. But both will be travelling in almost opposite directions in the next decades.