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Photographing a Meteor Storm
PHOTOGRAPHING A METEOR STORM
George Zay
May 1996
With the potential for at least two meteor showers reaching storm levels by
the end of this century, obtaining scientific information on them can be
problematic. After the 1966 Leonid storm, I still read hourly estimations
ranging from about 25,000 to 200,000. A far spread to accurately describe
the event. No doubt in reality, the numbers were great, and so are the
number of estimations. Just saying "many" has little scientific value.
Magnitude distributions follow a somewhat general pattern...that is, for any
given magnitude, there will be more of the next dimmer magnitude. If we are
only able to capture on film a range of magnitudes from about 0 and brighter,
the dimmer range can be somewhat deduced as well. Accurately photographing a
meteor storm has many rewards. If done with some forethought, you can have
an accurate record of what you saw to share for years to come, as well as a
scientifically useful document of the event. What follows is an effort to
satisfy both of these.
GUIDED OR UNGUIDED CAMERA: I personally prefer a guided camera, but will
most likely run an unguided as well. It doesn't really matter. But for an
unguided camera, It is very important that you know where the camera is
aimed. Make sure certain prominent stars are in your camera's frame ...at
least 6 stars. I recommend pointing towards some prominent constellation or
star pattern such as the Big Dipper or Great Square.
FILM: The choice of film is important. You want to record the widest
possible magnitude range and also be able to distinguish magnitudes with some
degree of confidence. This means you want the fastest possible film for the
light conditions expected and a film from which magnitudes can be reasonably
deduced. The film that satisfies all these conditions is Black and White
with ASA ratings of 400 to 3200. With color, magnitudes aren't very
accurately determined. If the sky is expected to be moonless and relatively
light free, I highly recommend T-max3200 film. About half the camera stores
will have T-max3200 stored in a back room refrigerator. If there is an
appreciable amount of moonlight (even a full moon) on the expected storm
nite, choose T-max 400 or Tri-X400 film.
CAMERA AND LENS: The most useful camera is an older 35mm Single Lens
Reflex(SLR). The newer electronic camera's won't cut the mustard. Their
shutter mechanisms are electronic. With a series of time exposures, the
camera's battery will soon be drained. Perhaps this may be discovered at a
moment when your work is incomplete? Anyhow, the shutter mechanism for most
older camera's is mechanical.
The lens of choice should be fast and non-telescopic. For possible storm
conditions there are two lens/f-stop combinations that I recommend. The first
is a typical normal 50mm lens with a useable f/stop range from about f/2 to
f/1.4. Meteor magnitudes expected to be photograph should be near 0. The
other possibility is a 28mm f/2.8 combination. It's area of coverage will be
greater than the 50mm, but the meteor magnitude threshold will be somewhere
near -2.
The meteor storms that may occur by the end of this century are the 1998
Draconids and the Leonids in 1998 and 1999. A meteor's velocity is a major
factor for what beginning magnitudes will be photographed. The Draconids are
slow while the Leonids are very fast. Fast meteors have a lesser amount of
time to expose film so the magnitude threshold will probably start near -1 or
-2. The slow meteor threshold will be somewhere near 0 magnitude.
EXPOSURES FOR A STORM: Using the 1966 Leonid storm as a referrence, I'd
recommend the camera being aimed about 35 degrees from the radiant. Then
centered at a 50 to 70 degree angle above the horizon as well. The peak of
the 1966 Leonid storm only lasted for about 40 minutes, while the remainder
of the night resembled a normal Perseid shower. On possible storm nights
under dark sky conditions, make 15 minute exposures until a 1/2 hour prior to
the radiant reaching the horizon. Then make 10 minute exposures for the rest
of the night until visual counting is not possible. At this point, make
exposures lasting 2 minutes each. Under bright moonlight conditions, make
all your exposures at 5 minute intervals. When visual counting is not
possible, make exposures lasting 2 minutes as well.
A helpful hint is to have a cassette recorder on hand to verbally
record all start/stop times and the camera's center of field. When you
record start/stop times, make sure the accuracy is to within + or - 1 second.
Also be sure to set your watch before the evening begins.
PHOTOGRAPHS FOR ANALYSIS:
If you are successful in photographing a meteor storm, it is now ready for
analysis. First you must write on the back of each photo the following
information:
# Date
# The exact beginning and end of exposure (+ or 1 sec; in UT)
# The approximate RA and Dec. of the Field of Center.
# Site location and it's geographic coordinates
# focal length and speed of the lens
# Film type (ASA, format)
# Observer's Name
For the analysis of such events it is expected that the International Meteor
Organization(IMO) will establish a research group devoted to such an
outburst. At that time I will be hearing from IMO regarding who to send the
information to and will be relaying it to those who contact me. Good Luck!
George Zay
GeoZay@aol.com