Message-Id: <v01530500af5e2df9802f@[207.90.162.215]>
Date: Tue, 25 Mar 1997 21:33:09 -0800
To: pinhole@exploratorium.edu
From: ronwong@unleashed.net
Subject: Re: Hale-Bopp morning AND evening
In response to Dave Porter's comment and question:
>
>It seems peculiar that Hale-Bop is ahead of the
>sun in the morning and behind it in the evening. Is this because of
>parallax?
>
It appears this way because of the way the heavens move about Polaris (the
North star). The comet and the sun have about the same right ascension
presently and the two appear to move counter-clockwise about Polaris. What
you see comes about because Hale-Bopp's declination is greater than the
sun's placing it closer to Polaris. Combine this with the rotation about
Polaris and you get what you've seen.
Take a pinwheel. Think of it's center of rotation as the position of
Polaris in the heavens. Position one of the arms so that it is below the
center of rotation. Since they have about the same right ascension, place
the sun at the tip of this arm and the comet at a point half-way between
the sun and Polaris (right now, the declination of the comet is about 45
degrees North while the sun is just above the celestial equator). Imagine a
card placed horizontally in front of this arrangement so that the comet is
a little below the top of the card and hidden from view. This is
approximately how things are around midnight. Rotate the pinwheel
counter-clock wise and you'll see the comet rise in the "east" before the
sun, cross the sky during the day with the sun, and then set in the "west"
after the sun.
Ron Wong