This image shows the geostationary satellite Cosmos 2172. It was a Russian communications satellite launched on 22/11/91. The satellite went out of service in 1996 so that its orientation in space is no longer controlled. This probably explains the brief brightening of the satellite trail in the middle of the picture which would occur as the Sun glinted off part of the rotating spacecraft. Cosmos 2172 was 35799km above the Earth when this picture was taken.

Technical Details

This image was obtained with a 10" LX200 at f6.3 and a Starlight Xpress HX516 CCD camera. The exposure lasted 25 seconds and the telescope was tracking with the stars which is why the satellite shows up as a trail.

The original frame has been calibrated using reference stars from the Hubble Guide Star Catalogue so that the precise co-ordinates of any point on the image can be measured. This also allows the frame to be rotated to match the north south co-ordinate axes surrounding the picture. The star marked S1 is GSC4853687 and is magnitude 14.6. The point marked with a cross is the predicted position for the satellite at 22:10GMT. This point is approximately 63 arcseconds from the satellite trail and this discrepancy is probably due to errors in the Keplerian elements for the satellite.

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