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Observing geostationary satellites

Greg Roberts

For the past 20 years I have been observing these satellites using either a 30 inch or 20 inch reflector at our Sutherland observing outstation of the South African Astronomical Observatory. This is not official work and I only do it on a casual basis when observing conditions are too poor for my normal astronomical observing. I have kept a list of satellites observable from my location but this has not been updated for several years now so is probably not of much use and I will try and update it as soon as possible.

Unfortunately the telescope used has a very narrow field of view-about 10 minutes of arc so unless the satellite is close to the equatorial plane I stand a good chance of missing it,especially if the inclination is more than a degree or so. With an image intensifier I can get down to about magnitude 15.5-16 on a good night. For those interested the technique is to park the telescope at the declination corresponding to the equatorial belt from my location - about 5.3 degrees North Dec, then use the telescope slow motion in hour angle to scan in Right Ascension. Once I locate a moving object I switch the telescope drive off then watch the stars drift through the field with the satellite stationary. By reading the telescope hour angle and declination circles I am able to determine the satellites position and hence sub-satellite point if needed. Although I havent done much geostationary satellite scanning in recent years- a result of getting old making me lazier ! - I will check out the published positions of military satellites etc and see what is there. With luck the satellite might be at a node and hence in my field of view, otherwise I will have to scan in declination as well as hour angle.

One interesting grouping I found recently was at the location for the ASTRA satellites. In my 10 minute arc field of view I can see 5 satellites simultaneously,two being brighter than the rest and one being somewhat fainter than the other four. What is even more interesting is that they drift relative to one another and I have actually seen one satellite merge with another. Looking at the orbital parameters there is only a spread of about 6 kilometres in altitude so I would think these satellites come very close to one another at times! Now as to brightness - when I first pick them up at the start of the night they are rather faint - perhaps magnitude 10 to 14 but at local midnight, when the phase angle at the satellites is about maximum I would guess they are about 2 magnitudes brighter.As dawn approaches they get fainter again so for those with small telescopes try and observe them at maximum phase angle. For me the satellites are almost on my meridian with an hour angle of 7.2 minutes west, so maximum phase occurs around local midnight .

"Technical" details are :

Norad catalog numbers 19688, 21139 ,22653, 23331 and 23686 corresponding to ASTRA 1A, 1B, 1C, 1D and 1E. Objects 19688 and 23331 appear to be the brightest and are suspected of being the two that merge every night. I suspect the faintest satellite is #22653. However I would imagine these satellites are all of similar if not identical size so the variations in brightness amongst them are due to reasons other than physical size.

Occassionally I have used the 20 inch reflector for viewing medium altitude satellites such as the GLONASS and NAVSTAR satellites.,but even then the satellites still rapidly whizz across the field of view . If Im quick enough, and press the slow motion controls in the correct sense etc I can actually follow these satellites . Using this same telescope I was able to track Apollo 11 and its assorted debri out to about 200 000 miles - the objects were easy and it was only the brightness of the moon that prevented me from tracking them further out, so that is my present "distance" record. (in those days the telescope was not fitted with an image intensifier). With todays large amateur telescopes and CCD cameras it should be possible to exceed this kind of distance with great ease.

next up previous
Next: Eurosom 2 Progress Up: No Title Previous: Flash information

Bart de Pontieu
Fri May 24 11:30:41 MET DST 1996