Re: [Phys-L] Comet ISON

[Bruce Sherwood <Bruce_Sherwood@ncsu.edu>]

Of course many objects including Polaris are visible before sunrise and
after sunset on the same day, but we're talking about an object (the comet
ISON) which is very near the Sun during these weeks and will (as far as I
can determine) never be visible at both times on the same day. It's
important not to tell people who want to try to see this comet that they
can go look for it after sunset.

Bruce


On Thu, Nov 14, 2013 at 3:49 PM, Paul Nord <paul.nord@valpo.edu> wrote:

> Consider only that the North Star is in the sky ALL the time.  For someone
> in the northern hemisphere, it never sets.  That should help to explain how
> something may be seen both before and after sunset.
>
> Here at about 40º N, there is a big chunk of the sky around the pole star
> which is always above the horizon.  Around that circle I can draw other
> circles which are in the sky "most" of the time and only set briefly at
> some point every 24 hours.  Some parts of the sky are above the horizon for
> 12 hours.  And some parts of the sky (e.g. southern constellations) never
> rise above the horizon.
>
> Paul
>
>
> On Nov 14, 2013, at 4:03 PM, Bruce Sherwood <Bruce_Sherwood@ncsu.edu>
> wrote:
>
> Good point, but judging from the images shown in Sky & Telescope, as ISON
> approaches the Sun it's near Mercury and Saturn in the sky, a bit below but
> near the ecliptic plane, so not visible after sunset. Then, something I'd
> missed in the article, the closest approach to the Sun is about Nov. 28, so
> close that it may disintegrate due to extreme heating and tidal effects. If
> it does emerge, the images shown for the first few days in December show it
> moving nearly vertical, so definitely not visible after sunset.
>
> Bruce