Solar transit by satellite

Rob Matson (
25 Jul 1996 11:41:04 -0800

No joy on EGP last night -- didn't get out of dinner in time!  I leave for the
Sierra Nevadas to go mountain climbing later today, so I'll run some
predictions for my various base camps.  Seeing should be excellent.  Tonite
I'll be staying at 8600' in the middle of nowhere, where naked-eye limit in
the past has been close to 7 (if you hyperventilate and pound vitamin A!) 
Unfortunately, there's the moon to contend with.  Tomorrow night I'll be at
around 10,600',
but the moon will be worse.

I wonder if there are any Seesaters out there with the equipment necessary to
do solar observations?  More specifically, an 8" scope (or larger) with a
full-aperture solar filter and an integrated video recorder.  The goal,
naturally, would be to capture a large satellite doing a solar transit.

A diffraction-limited scope with an 8" aperture has a resolving limit of about
3 microradians (about 0.6 arcseconds).  A 10-meter object at 500km subtends 20
microradians -- quite resolvable.  Of course, you need to know your site
latitude and longitude fairly accurately because the transit track is only
about 4.4 km wide for a satellite at 500km slant range.  If someone has the
necessary equipment and can give me their site coordinates, I can tell them
all the objects that will be doing transits on a given day (there are often a
dozen or more).

Alternatively, I wrote a program which can plot the ground transit track of a
given satellite against a map of the U.S. (or wherever).  That way, I can
determine which cities are close to the transit centerline of a large object
like Mir.  Wouldn't a silouette of Mir against the solar disk make an awesome
cover shot for Sky & Telescope?  --Rob