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Re: (meteorobs) Seeing the Geminids this year
On 5 Dec 2000, at 17:48, Lew Gramer wrote:
>
> HitTheRoadCarol@aol.com asks:
> >Does anyone know when the Geminid Showers will be able to be seen over
> >Las Vegas, Nevada?
>
Carol,
The short answer to your question about when is the best time to
watch for the Geminids meteor shower from near Las Vegas, NV is:
1.) 2:40am night of Dec 13/14 (+/- a few hours)
The next best time would be:
2.) 8:30pm - 9:30pm night of Dec 14/15
There are a few other decent times too, like:
3.) 2:40am night of Dec 14/15 (+/- a few hours)
4.) 7:15pm - 8:15pm night of Dec 13/14
5.) 2:40am night of Dec 12/13 (+/- a few hours)
The LONG answer follows:
There are 3 main factors that affect when and where a meteor shower
is best visible. They are:
1.) The date/time the shower is at maximum strength
2.) The height of the shower radiant above your horizon
3.) The background sky brightness
All of these contribute in changing ways with time and location.
The best time to observe occurs at the optimum combination of these 3
factors.
For the Geminids, the shower peaks out on Dec. 13th. However,
compared to many other showers it has a broad peak with pretty high
activity remaining a day before and after. (Some showers like the
Leonids have very sharp peaks that last an hour or so, and if you
are not looking at the right time, you miss all the action! )
But the Geminids are cool - they give you lots of chances.
The radiant is the common point in the sky (relative to the fixed
stars), if you trace back their path, from which the shower meteors
will appear to come from. The higher the radiant above your horizon,
the more meteors you will see. The Geminids radiant is at (7h 28m and
+33°) celestial coordinates, very near the bright star Castor in
Gemini. The reason 2:40am is the best time for you, is because that
is when this radiant is highest, in fact almost directly overhead.
Background sky brightness is composed of 2 factors:
1.) City lights
2.) Moonlight
You can remove #1 by driving as far out of town as you feel you can
go. Las Vegas is a very bright city for its size, but also it is
surrounded by unpopulated desert, so an hour drive will put you under
pretty dark skies. (If you don't know a good safe place to go, try
contacting your local astronomy club).
Moonlight is the main problem for this year's Geminids. The bright
full moon occurs just a few days before. In fact, the moon is located
right near the radiant! So, its tough to avoid it. However, the
reason 8:30 - 9:30pm Dec 14 is good, that is a "window of
opportunity" before the moon rises! The downside is the radiant
is at very low elevation in the NE (abou 20°). This reduces the
number of meteors you will see by a factor of 2.5 times. But,
without the bright moon washing out your sky, you also will see about
2.5 times more meteors, so the 2 effects cancel out!
REMEMBER - You must go out of town to a dark sky location, to benefit
from this dark window of opportunity!
Take note, the window before moonrise the night before is much worse,
because it rises earlier at 8:15. The hour before is moonfree, but the
radiant is so low (10°) the meteor numbers will be very reduced.
So, there is the whole story about the "best" time to watch the
Geminids. Take your pick, and Enjoy!
Mike Linnolt
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