The gegenschein is one of the hardest to observe phenomena in the sky. It is
similar to the dry-heiligenschein effect observed on Earth (the bright spot
around the shadow of an airplane, for example). But the gegenschein is
very faint, a few magnitudes fainter than the Milky Way. If you live anywhere
near a city or other light-polluted area, you will have no chance to observe
The gegenschein is one of the faintest phenomena to observe. It requires long
time exposures on fast film.
The gegenschein is best visible during September-October or February-March, while the antisolar
point or opposition point (the point opposite the sun) moves along the ecliptic in an area free
of the Milky Way. Observation times are best around local midnight, when the
sun is deepest below the horizon and thus the antisolar point with the
gegenschein around it, highest in the sky. Before you go out to observe,
look up the location of the antisolar point in a sky chart program, or try
to figure it out for yourself based on the inclination and position of the
ecliptic. This can be tricky for beginner observers, however, since the ecliptic makes an angle
with the equator. But it helps to know that in winter, at midnight, the antisolar point is
where the sun would be at noon in summer.
Go out to a dark location, and let your eyes adapt to the dark at least 20
minutes. The sky must be free of dust, clouds, and water vapor, and ofcourse
the night should be moonless. Bright planets such as Jupiter and Saturn should be
at least 90 degrees away from the point as well.1 After
scanning the approximate location of the antisolar point, you will see a
very faint glowing patch of light, approximately 10 x 20 degrees wide. You can
see it best when not looking straight to it, but look a few degrees away from it, as your
eyes are more sensitive for peripheral viewing.
Film & exposure settings
Needless to say, photography of this phenomenon requires a very fast film,
or very long exposure times. If the sky is not dark, photography of the
gegenschein is next to impossible. Use 1600 ISO film or faster, f/2.8 or
wider aperture, and exposure times of at least 30 minutes. Use a sturdy tripod
and cable release for the camera.
If you do not have a star-guiding setup, the stars will produce trails
on your photo, and after 30 minutes the gegenschein will start to blur
out as well, as it is (almost) fixed with the position of the stars for
any given night. Hence, use a wide-angle lens such as a 20mm or wider. If
you do have a guide system, you can best use 28mm or 35mm.
Note that the later you go out to observe, the darker and more clear the sky
generally gets, due to the cooling down of the atmosphere and the reduction of
the airglow. But also, the gegenschein will be at a lower elevation. I think the
best time to photograph this phenomenon is between 00h and 02h local time.