|Click image to return
Geostationary satellites are in the equatorial orbit at 36,000km altitude where the orbit period is 23 hours 56 minutes. This ensures that they remain in the same position in the sky as viewed from Earth. This image shows the Astra satellites at longitude 31.5 degrees E. Because the telescope is tracking the stars it is the satellites that appear as trails. Although nominally at the same position in practice they are maintained within a fraction of a degree of nominal.
Note the different trail followed by one of the satellites which moved about 0.012 degree south during the exposure. That is probably a defunct satellite for which the N-S station-keeping has been terminated. In other exposures its trail was seen to be varying in brightness.
Can you spot the two galaxies that were passing by the satellites at the time this image was made?
The satellites were imaged here using the piggybacked Sywatcher 100mm refractor and f6.7 focal reducer with the Starlight Xpress SXV H16 CCD camera. The width of the field of view is 1.4 degrees. Exposure was 30 seconds, during which the telescope moved 0.125 degree. [Jefferis]