Flares from Nadir normal surfaces

Robert H. McNaught (RMN@aaocbn2.aao.gov.au)
Sun, 08 Mar 1998 21:05:31 +1000

Since as of this moment Rob McNaught isnt a Seesat subscriber
This is posted for him[ 1035UT March 8]
From:	AAT40A::RMN          "Robert H. McNaught"  8-MAR-1998 19:12:55.93

Russell stated that for a satellite with a nadir-pointing surface to give 
a reflection, the Sun will be the same elevation below the horizon that
the satellite is above it (and in the same azimuth). 

These comments aren't quite correct, but are an approximation for low
satellites close to the observer (a flat Earth assumption).  I discussed
the geometry of Sun-pointing and nadir-pointing surfaces in "Reflections
on the flat surfaces of satellites" in Space 16/82 (30 Apr 1982); the
newsletter of the Earth Satellite Research Unit at Aston University in

I won't try to describe the geometry here, but it only involves adding the
center of the Earth to the picture, looking at complementary and suplementary
angles and a bit of trig.  In effect, as the satellite moves from overhead,
it tilts a nadir-pointing surface towards the observer making the solar
depression necessary for a reflection GREATER THAN the satellite elevation.
The obvious example is a satellite on the horizon.  The nadir pointing
surface must point below the observer (to the centre of the Earth).  If the 
observer-satellite-Earth centre angle were "alpha" deg, then the Sun would
have to be 180- 2 * "alpha" deg below the horizon.  This example is simple
because the satellite elevation is zero.

The above mentioned notes were further discussed in Space 17/82, a week
later, with more examples and a correction to an example from the previous
week.  Examples discussed were 78-64A Seesat, one of 80-19C,D,G NOSS? and
81-85A Big Bird (which Russell himself had seen at -7 to -8!).

Cheers, Rob McNaught