Satellites in transit

R.B. Minton (
Thu, 25 Jul 1996 14:49:11 -0600

Regarding observing satellites in transit....  I used to photograph Jupiter's
satellites with a 61" reflector when they were in transit across Jupiter's 
disk.  I found it was easier to record detail on the satellite when it was
against a background that was about the same brightness as it - compared to
photographing it against a dark sky.  The reason is irradiation which affects
both the eye and the photographic emulsion (and probably a CCD too). 
The irradiation makes the smaller object either smaller or larger depending if
it is against a dark or light background - it also screws-up the outline of the
object (like changing a circle into an ellipse - because of the brightness 
profile of the object).
My suggestion would be to photograph a satellite against the moon and use a
varying solar elongation (from the moon) to change the illumination of the 
I can attest to the validity of this method because I was credited with being
the first person to photograph the red polar caps of Jupiter's satellite "Io";
and an account appeared in the Smithsonian Magazine many, many years ago (25?).

R. B. Minton
If you can't see it, photograph it.