Synodic effect
Björn Gimle (b_gimle@algonet.se)
Wed, 12 May 1999 15:04:06 +0200
Rainer Kresken:
> Shouldn't it be possible to derive the spin direction from the "synodic
> effect" ?
> Depending on the spin direction, the flash time offset from a constant
> period
> should be either positive or negative. Or not? Am I wrong?
>
Yes, the difference is proportional to the rotation period * the angular speed of apparent motion,
so for a LEO it should be possible to find the magnitude and sign of the deviation during a pass.
Perhaps better if we observe one pass in the east, one in the west the same night, or during the same orbit by two observers on the opposite sides of the ground track.
But we must be certain that we are comparing a full cycle, that is NOT half, third... cycles !
If so, the relative magnitude of shift, should be related to the sine of angle between the rotation axis and the APPARENT orbital plane. But we still have one-dimensional information (magnitude) so we don't know where it is pointing, unless we can piece it together from several different geometries.
For a GEO, the effect does not vary much during a (short) night, because of the slow and nearly uniform motion of the observer-satellite vector (and satellite-Sun).
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