RE: mir - wavering in its path

Ted Molczan (molczan@home.com)
Sat, 11 Sep 1999 17:40:24 -0400

> I observed Mir this morning.  I have never seen a satellite
> do what it did
> this morning - it seemed to deviate from its path, almost
> undetectably -
> sort of like it was wavering back and forth like a very
> shallow sine wave.
> Was this an optical illusion or did I actually see it happen?

This is a common optical illusion. I found it most pronounced when observing
bright, slow-moving satellites, like the old Pageos balloon, which is no
longer in orbit. Terence Dickinson offered this explanation in his astronomy
field guide, NightWatch:

"Whether satellites have a steady or fluctuating brightness, most novice
observers agree that they do not appear to move across the sky in perfectly
straight lines. There seems to be a perceptible waviness to their paths, a
jerkiness in speed as they glide through the starry background. In fact,
these oscillations are in the mind, not the sky. The satellites actually
move in precise linear paths at an even velocity.

The human brain likes to link patterns into a recognizable image. This is
done instantaneously in daily life. However, looking at one moving light in
a randomly dotted black sky, the brain constantly tries to produce these
patterns but fails. What are thought to be oscillations in the satellite's
path are really the unconscious workings of the mind trying to make sense
out of an unfamiliar visual environment. The result is, in effect, an
optical illusion."

Ted Molczan