Is there a chance for the many geostationary satellites to enter into the moon’s shadow?

If so, how frequently do such eclipses happen and how long do they typically last?

Are such eclipses pre-calculated and the satellite is programmed to handle such events (e.g. sudden drop in temperature associated with eclipse, etc)?


1 Answer 1


You can get an approximate answer by looking at how often a solar eclipse crosses the equator. This map for the years 2021 through 2040 implies that satellites around 30 W longitude will experience a deep partial eclipse 5 times during that time period. (2023, 2033, 2028, 2034, 2038). The maximum duration of a total solar eclipse on Earth is just over 7 minutes long, so the duration at geostationary orbit (slightly closer to the Moon) is only slightly longer. Of course, a solar eclipse causes by the Moon only affects the few satellites in the path.

Eclipse paths 2021-2040 From NASA Solar Eclipse Page

A bigger problem are the eclipses that occur each year when all of the geostationary satellites pass through the Earth's shadow. These occur for a few weeks around the March and September equinoxes. At the date of maximum eclipse, the duration is 72 minutes. See Intelsat Eclipse Season.

I would hope that satellite needs no special programming to handle these Earth eclipses. The satellite either gets power directly from the solar cells or battery. It should not need to know that an eclipse will occur and therefore do something different. Therefore, the infrequent lunar eclipses should not require anything special.

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    $\begingroup$ This is a good answer but I would like to add that geostationary satellites absolutely do have special behaviours to deal with earth eclipses and lunar eclipses. They are highly optimised to operate in 100% sunlight and require certain actions to prepare for entry and exit from eclipse. For example solar panels generate more power when colder, since they get very cold during eclipse they cannot left connected during the exit from eclipse because the power surge is too great. Their temperature is allowed to return to normal before they're re-connected. $\endgroup$ Aug 21, 2020 at 10:32
  • $\begingroup$ Thanks @PeteBlackerThe3rd. That is interesting. Are those provisions based on some date and time so that the satellite knows it is going through an eclipse, or it is just based on reacting to what is happening? In other words, if the satellite goes through a solar eclipse caused by the Moon, does it respond automatically because it is programmed in general to handle solar eclipses (caused by the Earth), or would the satellite need to know that it is experiencing something different? Either you or I can edit the article based on your suggestion. $\endgroup$
    – JohnHoltz
    Aug 21, 2020 at 16:43
  • $\begingroup$ Satellite ground controllers will have predicted exactly when eclipses caused by the earth or moon will occur. The required commands to deal with these eclipses will be uploaded some time in advance. These satellites are worth a great deal and are closely controlled by their operators. Maybe one day they'll be more autonomous and able to predict their own eclipses, but as far as I know we're not there yet. $\endgroup$ Aug 22, 2020 at 9:23

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