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I was watching a video on an 80s era satellite TV and it mentioned that the channel would occasionally stop broadcasting due to an "eclipse".

Only if you absolutely must, skip to 18:12 for the bit about the satellite eclipse in this video:

What does this mean? A geostationary satellite is always going to be visible to everyone on the same side of Earth and there's no objects in orbit between us and the geostationary ring that would cause more than a momentary blip in the signal.

(I've tried searching but everything I've found talks about lunar or solar eclipses.)

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    $\begingroup$ Sometimes from your point of view the Sun passes behind the satellite that your dish is pointed at. This causes interference with the signal from the satellite. Apparently the amount of interference can be effected by solar weather, like flares and sunspots. I think a proper answer would mention some examples of geosynchronous alt/azimuth and how the Sun can momentarily line up with that position at certain times of the year. If you can mention at least your city someone could probably use your location as an example. I would do it but several people here are better than I am with diagrams. $\endgroup$
    – Steve Pemberton
    Commented Aug 31 at 17:24
  • $\begingroup$ Kudos for the video find, what a gem! Also, how cool that Phillips actually "sponsored" the eclipse with creepy advertisements before and after it. Sometimes I really miss the 80's. $\endgroup$
    – uhoh
    Commented Sep 1 at 0:53

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They are referring to the sun being eclipsed from the GEO satellite as it passes through the Earth's umbra. If the GEO satellite does not have enough battery reserve, it will need to stop broadcasting temporarily.

enter image description here

The sketch makes it appear eclipses would occur every orbit. But the satellite's GEO is aligned with the Earth's rotational axis, not its orbital axis. As a result, the satellite's GEO orbit is not coplanar with the Earth's orbit. Satellite eclipses are most frequent and last the longest during the equinoxes. The same is true of lunar eclipses, for similar reasons.

Eclipses are not limited to geosychronous orbits. Non-polar LEO satellites are "eclipsed" for less than 50% of their orbit when they pass over the Earth's night side. The sketch below shows the relationship of umbra (total eclipse) to the penumbra (partial eclipse)

enter image description here

The next sketch shows a satellite with a LEO perpendicular to the terminator (sunset line)

enter image description here

As the satellite progresses a-b-c,, the intensity of solar radiation on the panels decreases.

The next sketch shows a satellite with a LEO coplanar with the terminator. It experiences no eclipse

enter image description here

You can observe the LEO eclipse yourself. Pick a low-inclination satellite travelling west to east across the evening sky. At some point, after passing overhead, it will dim as it passes into the penumbra, then disappears quite suddenly as it hits the umbra. If you follow a succession of satellites, you will notice the "line of disappearance" is roughly along a celestial meridian. The line will slowly march westwards until midnight, when there will be no visible satellites. Then satellites will start appearing in the eastern sky.

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    $\begingroup$ Ah! It's the satellite's solar panels going into Earth's shadow. The satellite is still visible to us but it didn't have enough electricity to relay the broadcast. That makes sense. $\endgroup$
    – billpg
    Commented Aug 31 at 18:35
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    $\begingroup$ I guess modern TV satellites have big enough batteries that it's no longer an issue? $\endgroup$
    – billpg
    Commented Aug 31 at 18:36
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    $\begingroup$ I found this article which says: Between 28 February and 11 April, and between 2 September and 14 October, roughly 21 days either side equinoxes, satellites in geostationary orbits will pass through the shadow of the Earth once every day. While in the Earth's shadow the satellite gains no power from its solar cells. The time spent in the Earth's shadow increases to a maximum of about 70 minutes right on the equinox. Batteries are one of the main limiting elements in the lifetime of a broadcast satellite. $\endgroup$
    – Steve Pemberton
    Commented Aug 31 at 19:48
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    $\begingroup$ There are also Sun transits when a geostationary satellite transits the Sun. This also happens around the equinoxes, and can cause interference unrelated to solar power. (The Wikipedia article I linked to may not be the best source) $\endgroup$
    – Steve Pemberton
    Commented Aug 31 at 20:03
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    $\begingroup$ @uhoh - true they would not reflect nearly as much heat as a reflective surface. But it would likely get somewhat hotter than ambient temperature during a transit. DTH (direct to home) dishes for some reason are usually gray. Actually I think most people don't realize that you can paint a DTH dish, I painted mine the same color as my house so that it doesn't stand out as much. You just have to avoid painting the plastic cap that covers the LNB (the antenna). $\endgroup$
    – Steve Pemberton
    Commented Sep 2 at 2:02

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