The solar eclipse of July 11 – as seen by AO-51

On July 11, 2010, a total solar eclipse could be observed in the southern Pacific Ocean. During the eclipse, the AO-51 amateur radio satellite was entering daylight, coming in over South America.

When AO-51 enters daylight the solar arrays start charging the batteries. This can be observed in the telemetry as a sudden increase of the current from the solar arrays. This time; however, a sudden drop in the current was observed shortly after the current started to increase, see the graph below.

The time and place where this unexpected drop occurred suggested that the satellite might have experienced the solar eclipse that was about to happen over the southern Pacific. It was Masa san, JN1GKZ, who noticed this and reported it on the AMSAT BB where after Mark, N8MH sent out the telemetry graph shown above.

A quick simulation using the Celestia space simulator confirmed that this was indeed the case. The video below shows how it may have looked like from the satellite.

Watch on Youtube or download H.264 encoded .mov file (~100MB).

You can try it for yourself. Celestia is available as free download from – it’s a great space simulator for demonstration and educational purpose. You will have to add the data for the satellite. You can use my data to begin with, download from here:

Unpack the file to the “extras” folder of Celestia, start the program and find AO-51 (type ENTER, AO-51, ENTER, then press “g” to go to the satellite). Enjoy!

Author: Alexandru Csete

Embedded software engineer in the satcom industry during the day. Radio amateur and SDR hacker during the night.