Re: Phase Angle

Jim Varney (
Tue, 23 Sep 1997 23:05:21 -0700 (PDT)

---"Sue J. Worden" <> wrote:

> 	Is not the QuickSat "sun-object-observer angle", i.e.,
> 	angle sun->satellite->observer, the same as the Jim's
> 	"angle subtended from sun to satellite to observer"?
> 	I am very confused at this point.  I would appreciate
> 	someone shedding some light on this, and at full phase
> 	illumination, please. :-)

No, you're not confused, I was.  I confused "phase angle" for "phase,"
as in lunar phase = % illuminated.  I got into the habit of ignoring
both the phase and phase angle as useful quantities because most
satellites don't show that much brightness variation due to phase.  I
guess I got so good at ignoring phase and phase angle I forgot their
respective definitions.

I do apologize to anyone I may have confused!

And Richard Clark is correct: phase angle is a 2-D angle subtended
between two 3-D vectors, while the az-el quantities are 3-D because
they are in essence unit vectors.  Whew.
Jim Varney   121.398W  38.458N 8m   Sacramento, CA,

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