Brian Tung wrote:
Marty wrote (about geosync sats):
Cool! I've never (knowingly) seen one of those...

The geostatationary satellites (a subclass of geosyncs that stay more or
less above the same spot on the Earth's equator) cluster around the
celestial equator, for what I hope is a reasonably obvious reason, so
looking just south of the equator if you're in the northern hemisphere,
or just north of it if you're in the southern hemisphere, will allow you
to pick one up eventually. I've seen a couple of them while observing
the Trapezium.

Puzzle: Estimate my latitude.

Answer #1: google isi.edu, see that it's in Marina del Rey, CA =
latitude is about 33 degrees. ('Tis a shame Google Maps lacks lat/lon
grids....)

Answer #2: Geosynchronous radius is R = sqrt (GM/n^2), with
GM = 398600 km^3/s^2, n = 2pi/86164 radians/sec, so R = 42164 km.
Declination of the Trapezium is -5.4 degrees. I'm not going to
try an ASCII plot, but it's obvious that
tan Dec = -r sin lat / (R - r cos lat)
with r = Earth's radius (assuming a sphere) = 6378.14 km.
The solution is
lat = Dec - arcsin (R sin Dec / r)
= +33.07 degrees.

Thanks for giving me a little bit of fun this evening.

-- Bill Owen

P.S. I've seen a geostationary satellite show up in my pictures too.
Nice straight line running e-w, and if you take the same field one
sidereal day later, it'll still be there. Perplexed the heck out of
me until we figured out what it was.