(meteorobs) Viewing the 2004 Geminid Meteor Shower

Robert Lunsford lunro.imo.usa at cox.net
Thu Dec 9 15:02:47 EST 2004

The Geminid meteor shower will provide a fine view of celestial fireworks 
this weekend and beyond. The expected time of maximum activity will be near 
22:20 Universal Time (courtesy the I.M.O.) on Monday, December 13. This time 
is favorable for Eastern Europe, the Middle East and Western Asia. Actually, 
strong rates are possible twelve hours either side of this time, meaning 
that everyone north of the equator will still have a chance of seeing an 
impressive shower. Those observers located south of the equator can see some 
activity near 0200 local standard time, when the radiant rises highest into 
their northern sky. Observers south of 30 degrees south latitude are out of 
luck as the radiant will not rise into their sky at all.  For observers in 
North America, the best rates will be seen Monday morning near 02:00 local 
standard time. This will be the best time regardless of what state or 
province one is located. After maximum activity the Geminid rates rapidly 
fall and by Thursday, December 16, the shower will have fallen below the 
level of the sporadic background.

This is one of the few showers that produce decent activity during the 
evening hours. The radiant, located five degrees northwest of the bright 
star Castor (Alpha Geminorum), rises near 18:00 (6:00pm) local standard 
time. You must remember though, at this time the Earth (the horizon and 
below) will block a great majority of the Geminid activity. Those that do 
appear in the sky at this time are just skimming the upper regions of the 
Earth's atmosphere. Therefore they avoid the dense lower layers of air. This 
allows the Geminid meteoroids to last much longer than they would if they 
struck the Earth at a more direct angle. From the ground one would see these 
meteors as long, majestic streaks lasting several seconds. These are 
commonly known as "Earth-grazers" and occur for all showers. Only the 
strongest annual showers produce enough of these meteors to make it 
worthwhile to attempt to view at this hour. Luckily, the Geminids are one of 
these showers. These "Earth-grazers" most often appear low in the northeast 
or southeastern skies. Occasionally, one will appear high in the sky and the 
sight is memorable.

As the night progresses, the Geminid radiant rises higher into the eastern 
sky. As the radiant gains altitude, the number of meteors lost to hills and 
trees lessens. One will also notice the average Geminid meteor becoming 
shorter as they strike the Earth at a more direct angle. By 22:00 local 
standard time (10:00pm) the radiant lies approximately half-way up in the 
eastern sky. It is near this time the action really increases. On the 
evening of December 12, at 22:00 one would expect to be seeing 20-25 
Geminids per hour from dark sky sites. This rate will increase and peak near 
02:00, when the radiant lies highest in the sky. No one knows exactly what 
the peak rates will be. Those observers located in areas where the peak 
occurs with the radiant high in the sky should experience counts in excess 
of one hundred Geminids per hour. Others will experience rates between sixty 
and one hundred per hour, depending on their longitude and weather 
conditions. After 02:00, Geminid rates will begin to fall and will continue 
to fall until the onset of dawn.

The Geminids occurring before maximum activity are normally dim. Therefore 
do not expect to see good rates this weekend unless you view from rural 
locations far from city lights. The Geminids seen after maximum are usually 
brighter but unfortunately rates descend rapidly therefore there will be 
less of them to see. To see the most activity it would be wise to view from 
midnight to 0300 local standard time on Monday morning December 13. It is 
advisable to sit in a comfortable lounge chair and face halfway up into the 
sky. At this time of night the Geminid radiant will be high in the sky for 
observers in the Northern Hemisphere. Therefore meteors will be appearing in 
all directions so it would be wise to face toward the darkest and least 
obstructed direction. All Geminid meteors will appear to trace back near the 
bright star Castor, in the constellation of Gemini. Another slightly 
brighter star (Pollux) lies only five degrees to the southeast. The 
brightest object in this area of the sky will be the planet Saturn, which 
lies in eastern Gemini on a line from Castor to Pollux, roughly the same 
distance that Castor lies from Pollux. There are other weak meteor radiants 
active at this time adding to the activity one will see. There are also 
sporadic (random) meteors that occur throughout the night. At this time of 
year one could expect to see up to twelve sporadic meteors and perhaps one 
or two meteors from other active radiants per hour.

There are interesting projects one can undertake while viewing meteor 
showers such as the Geminids. The basic experiment is to see how many 
meteors you see each hour. One can also collect scientifically useful data 
by categorizing each meteor and assigning an estimated magnitude for each 
one. You also would need to estimate the faintest star you can see during 
each hour so that scientists can calibrate your viewing conditions verses 
other observers. Experienced observers also record the time, velocity and 
other useful data such as the appearance of a persistent train. For more 
information on observing techniques visit the following web pages:




Unlike the Leonid and Perseid meteoroids, the Geminid meteoroids strike the 
Earth at a perpendicular angle. The streaks they leave in the sky often last 
as long as one second or more. This is good news for photography buffs as 
this makes it easier to capture Geminid meteors on film. All you need is a 
camera capable of taking long time exposures. You will need exposures up to 
fifteen minutes long, depending on the darkness of your night sky. A typical 
50mm f1.8 lens is fine and has produced many impressive meteor photos. I 
personally like to use a wider field lens such a 24 or 28mm. These lenses 
are not as "fast" as the typical 50mm lens but you can make up this deficit 
by using a high speed film such as ISO 800 or above. To capture a meteor 
just aim you camera approximately half-way up in the sky and then lock the 
shutter open. Stars will appear as parallel trails across the frame but a 
meteor will bisect these trails and will appear as a streak with sharp ends 
while the star trails appear blunt. You can eliminate the star trails by 
using a motor-driven mount. This mount may be especially designed for 
cameras or one can take advantage of your telescope's mount and attaching 
your camera directly to the tube of your scope.  Don't use the telescope 
itself to attempt to photograph meteors as the field of view is much too 
small and the chances of capturing a meteor will be extremely remote. There 
is also no advantage of using color films other than seeing the different 
star colors. Those viewing from rural areas can take exposures up to fifteen 
minutes long while those viewing closer to town should limit their exposures 
to five minutes. It all a matter of luck if any meteor passes through the 
cameras field of view. Using normal techniques, meteors must be at least as 
bright as first magnitude to be photographed. From previous experience I 
have found that I average 2-3 meteors per 24 exposure roll of ISO 400 during 
the Geminids.

This may be your last opportunity to view a major annual meteor shower in 
all its glory for quite some time. Many of the major showers are spoiled by 
moonlight in 2005. Next year a full moon will spoil the Geminid show 
therefore don't pass up this opportunity to view and photograph this shower 
under optimum conditions.

Clear Skies!

Robert Lunsford 

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