ISS transits

Witness an International Space Station (ISS) transit on a rear projection screen .

Using a rear projection screen made from inexpensive parts, several people can gather around a telescope and witness a transit of the International Space Station across the sun.

This excerpt from an ISS Transit Alert indicates a solar transit will occur September 7 at 12:28:41 local time. The centerline is 0.5 miles away from the home site, but the observer can be up to 1.4 miles away and still see a chord of the ISS travel across the sun's surface.

Minimum transit distances during the current reporting period:

Sun 0.5 mi

A - travel distance (miles) and direction B - date C - time (hhmmss) D - elevation angle of the ISS E - azimuth angle of the ISS ( + is East from North; - is W from N) F - range (miles) G - latitude for observing the transit H - longitude I - elevation above Mean Sea Level (meters) J - how far (miles) can I be from the centerline? (i.e., angular error = 0.25°)

For other than solar transits:

K - lunar transits: is space station sunlit?

planetary encounters: 1=Mercury; 2=Venus; 4=Mars; 5=Jupiter; 6=Saturn L - sun elevation angle M - sun/moon or sun/planet separation angle

A------- B----- C----- D--- E----- F--- G------- H-------- I--- J---- K L---- M----

9.0 SW 7 Sep 122839 54.1 173.8 263 41.6609 -86.3077 215 1.4

4.4 SW 7 Sep 122840 54.1 173.9 263 41.7034 -86.2378 227 1.4

0.5 E 7 Sep 122841 54.1 174.0 263 41.7457 -86.1679 244 1.4

[other data snipped]

The rear projection screen is mounted on the reflector telescope, whose aperture is stopped down. A white light solar filter is on the smaller refractor telescope.

Moments before the scheduled transit, the video camera was ready on a tripod--except for having charged batteries.

Below are a few shaky frames I grabbed from my hand-held camera in its video mode. Through the projection screen, the shape of the ISS is less defined than when looking through a 60 mm refractor with a solar filter. A friend using the refractor readily described the “wings” of the ISS as if it were a fly moving across the field of view. The view is decidedly better through a scope lens than on a projection screen, but then you’re limited to just one person at the viewer.

The ISS appears in the lower right corner of the sun, about 4:30 on the clock, and moves to the left. The dot near 6:30 is a large sunspot, while above it is a faint, indistinguishable sunspot group. The other visible marks are lint and dirt that I did not remove in time for the transit. In person the contrast is better than on these low-resolution images.

Thank you, Don and Mary, for your onsite participation in the September 7, 2006, transit.