Re: [Phys-l] Comets

[Chuck Britton <cvbritton@earthlink.net>]

How would this stack-up as an extreme scenario for 'fastest comet'. 
(shortest viewing time)

A highly elliptical orbit with apogee (closest?) occurring at one AU, 
(93+ megamiles or so), with the earth in the same neighborhood.
Let it's orbit be clockwise around the sun (earth's being counterclockwise.)

The more eccentric the orbit - the less time it spends in view.

Someone with way more experience with celestial mechanics than I can 
probably calculate a reasonable time for such a comet to come and go.

Let it come no closer than a few moon-orbit-radii to avoid another Tunguska.

Can anyone come up with a faster scenario?


At 5:51  -0500 on 12/10/06, R. McDermott wrote concerning Re: [Phys-l] Comets :
> ----- Original Message -----
> From: "John Mallinckrodt" <ajm@csupomona.edu>
> To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
> Sent: Sunday, December 10, 2006 4:47 PM
> Subject: Re: [Phys-l] Comets
>
>
> >  On Dec 10, 2006, at 11:29 AM, JMGreen wrote:
> >
> > >  With what speed can a comet appear to move?
> >
> >  Anything, including comets, can appear to move at any speed.
> >
> > >  Can it move across the sky from East to West in several days?  Weeks?
> >
> >  Yes.
> >
> >  But in all seriousness (not that the above wasn't), isn't it clear
> >  that the time it takes comets to "move across the sky" depends almost
> >  entirely on how close they are to us.  Nearby comets are moving at
> >  speeds measured in the 10's of km per second relative to us or any
> >  other nearby things.  So one that is a typical 100 million km away
> >  from us will take a typical couple of months to move across the sky.
> >  One that passes 10 times closer would take on the order of a week.
> >  One that passes 100 times closer (on the order of the distance to the
> >  moon) would take on the order of a day.
>
> The other question is, do you mean from when one first sees the comet?  One
> coming very close to us would still be visible for some time (weeks at
> least) before getting close enough to exhibit significant lateral motion.
>
> >  And when you see one moving across the sky in an hour or less, count
> >  your blessings.
> >
> >  John Mallinckrodt
>
> Indeed!
>
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