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Re: (meteorobs) Sino-Dutch Leonid Expedition 1998
Louis,
Below is a little ditty that I wrote a while back that you might be able to
use.
George
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PHOTOGRAPHING A METEOR STORM
George Zay
Revised: August 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 re-
wards. 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.
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 that can be
easily identified. 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 satisfied 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 moon-
less and relatively light free, I highly recommend HP-5 film
pushed developed for ASA 3200. If there is an appreciable
amount of moonlight (even a full moon) on the expected storm
night, use HP-5 developed for 400 ASA. You can also use T-max
400 or T-max 3200 films as well.
CAMERA AND LENS: The most useful camera is an older 35mm Sin-
gle 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 pos-
sible 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/1.8. Beginning met-
eor magnitudes expected to be photographed should be near 0 or
-1. 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 1998 and 1999 Leonids. A met-
eor'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 ref-
erence, 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 un-
til visual recording is not possible. At this point, make
exposures lasting two minutes each. Under bright moonlight
conditions, make all your exposures at 5 minute intervals.
When visual recording is not possible, make exposures last-
ing 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 photo-
graphing a meteor storm, it is now ready for analysis. first
you must write on the backs of each photo the following in-
formation:
# Date
# The exact beginning and end of exposure (+ or - 1 sec; in
UT)
# The approximate RA and DEC of the Center of Field.
# Site location and it's geographic coordinates.
# focal length and speed of the lens
# Film type (ASA, format) and the emulsion rate developed
for.
# Observer's Name
For the analysis of such events it is expected that the In-
ternational Meteor Organization (IMO) will establish a re-
search group devoted to such an outburst. At that time I
will be hearing from IMO regarding who to send the infor-
mation to and will be relaying it to those who contact me.
Good Luck!
George Zay
GeoZay@aol.com