Geostationary Satellite Eclipse

Geostationary satellites orbit the Earth in relatively constant sunlight except for a few brief weeks around the vernal and autumnal equinoxes. During those times the satellites will dip into the shadow of the Earth for roughly and hour each night.

Geostationary satellites are hard to photograph because they are extremely far away, roughly 22,000 miles above the equator. For reference the space station is only about 250 miles above the Earth. These geostationary satellites are usually a brightness of +8 or dimmer, but during the equinox they can be brighter and sometimes they can catch the light just right and flare up to naked eye brightness.

These satellites are a favorite target of mine because they don’t move in the sky, I can point my telescope (which doesn’t have any tracking motors) and leave it alone. On March 16th I stayed up later than normal to try and catch three adjacent satellites falling into the shadow of the Earth.

I collimated and focused the telescope, found the spacecraft in the sky, selected exposure settings that looked good, and left the camera to take pictures every 10 seconds for as long as possible. It turns out that my camera battery couldn’t handle the nearly two hour photo session, so while I didn’t see the spacecraft coming out of the eclipse, I did catch them disappearing into the shadow of the Earth.

All the images were taken with my Fuji XA2 camera connected to my dobsonian telescope with a T adapter and 2x Barlow lens. I used a ten second shutter speed and ISO 5000.

Geostationary satellites are kept in boxes defined by their longitude. These three satellites are 0.2 degrees apart, with AMC-16 at 85W, XM-3 at 85.1W, and XM-5 at 85.2W. At this orbital height a spacing of 0.1 degrees means they are spaced roughly 45 miles apart from one another, but they have some leeway to drift within a specified distance of their specified location. Obviously when I took the pictures they weren’t spaced very evenly.

Once I had all the images I was able to combine them in StarStax software to create an image of the background stars streaking by. This is usually a difficult image to get to look clean because any vibration in the telescope due to wind will cause the star streak to wiggle. I did some color adjustments and some touching up in DarkTable and GIMP to make it look cleaner.

Next I put all of my images into windows movie maker to make a time lapse animation of the eclipse. I love how this came out, especially how you can see shadow moves east to west (left to right in my image) by the slight time delay in each satellite going dark.

That video goes by a little quick, so I also made a slower time lapse of only the ten minutes at the eclipse.

The progression is easy to see when we break individual frames into a collage.

I might try doing a version of this shot again in a few days but without the telescope. I've seen examples of people taking night sky time lapse but you can briefly see the individual satellites as they flare to naked eye magnitudes. None of these satellites flared this time so first I'll have to figure out when those usually happen.