Geostationary Satellites

July 2017

One of the fun things I did as a visual observer was to observe the Geostationary Satellites. From Northern California these are positioned quite close to Messier 11. Of course, Messier 11 moves as the sky rotates. The satellites either appear as stationary dots with the stars moving past them (view from a dob) or as retrograde dots (from tracking mount). As long as you view them close to astro dusk they are quite easy to see visually.

Photographing them proved more of a challenge. My first attempt was to capture them with M11 in the field. Unfortunately the satellites appeared only as grey blobs (if that is what the blobs were) instead of visible tracks. My second approach was more successful. I slewed the scope to a particular Alt/az by using the SkyX to calculate the RA/Dec. I then turned off tracking. A 6 minute exposure was enough. After several runs I decided the best approach was to slew the scope by a fixed offset of 2 degrees and sweep the band from about 142 to 168 azimuth. The Declination was about -6 degrees. The actual altitude varied with the azimuth.

Timing is also important. While the satellites will see the sun for longer from their altitude and latitude, they will eventually be in shadow. Therefore I imaged from mid way through nautical dusk (about 21:45) through about 1 hour after astronomical twilight (about 2300).

The Sky allowed me to identify which satellite was which dot. While I will not guarantee 100% accuracy, these identifications should be close.

In the image below scroll to see the full band. The azimuth markings at the top of the image should be close. The streaks are stars that happened to be at that azimuth during the exposure.

Processing the Images and building the Mosaic

I recorded the images by slewing to an initial RA/Dec and then using ACP to move the frame about 2 degrees east or west. I recorded the nominal center of the image in the file name. This allowed enough overlap when I built the mosaic

The images were calibrated using Pixinsight. Unfortunately Pixinsight is not able to build a mosaic like this. So I had to use Photoshop CS 64 bit on Windows. The eventual frame was about 20,000 pixels wide.

Zoomify is used to convert the image for display

Copyrights For Photos

(c) 2017 Robert J Hawley.
Except as noted,all work on this site by Robert J. Hawley is copyrighted under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. This permits the non commercial use of the material on this site, either in whole or in part, in other works provided that I am credited for the work.

7/27/17