Photographing the International
Space Station
Forrest M. Mims III, Editor
The International Space Station (ISS) is so large that
the sunlight it reflects toward the Earth is highly
visible for an hour or so before sunrise and after sunset.
The Space Station is so bright that
it is easily photographed with a camera mounted on a
tripod, which is how the images in Figs 1-3 were made.
Figure 1 is a 10-second time exposure
that shows the track of the ISS from northwest to southeast
over Geronimo Creek Observatory in South-Central Texas,
the field from where I have made many thousands of sun
and sky measurements since May 1988. The image has been
processed to remove noise caused in part by bright moon
light.
The stars in the original, unprocessed
image are very slightly oblong. This occurred because
the camera was fixed and the rotation of the Earth caused
a slight apparent motion of the stars even during the
brief 10-second time exposure.
Figure 2 is a second 10-second time
exposure that shows the ISS as it enters the Earth's
shadow and disappears from view. The dimming of the
ISS begins as the rays of sunlight that illuminate it
begin to graze the top of the atmosphere. The dimming
rapidly increases as the rays of sunlight pass through
increasingly thicker layers of atmosphere. Figure 3,
a cropped version of Fig. 2, shows the dimming effect.
A careful analysis of the intensity
of the ISS light trail as it passes into the shadow
of the Earth would permit layers of aerosols to be identified.
This would make an interesting study should there be
another major volcanic eruption that contaminates the
stratosphere with particulate matter.
Many kinds of film and digital cameras
can be used to photograph the ISS, but a camera with
a time exposure capability will provide the best results.
Both Figs. 1 and 2 were acquired using
a tiny Casio EX-Z850 8.1 megapixel camera set to its
shutter priority mode. The flash was disabled, the ISO
was set to 200, and a 10-second time exposure was selected.
It was impossible to see the ISS through the camera's
tiny viewfinder or on its very bright LCD display. Therefore,
the camera, which was mounted on a tripod, was pointed
in the general direction of the satellite, and the shutter
was released. Six separate exposures were made, and
all captured a full ten-second trace.
For information on when the ISS will
be visible over your location, see NASA's Human
Space Flight web site. 
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