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We are all familiar with seeing low-Earth orbit satellites scooting across the sky in a couple of minutes. Many of them are bright and readily identifiable with the naked eye. Geostationary satellites on the other hand are much further away and would remain fixed in position (though moving very slowly with respect to the background stars).

How bright are geostationary satellites in reflected sunlight? Can any of them be spotted, even with a telescope?

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How will Starlink affect observational astronomy?

How do satellites impede current telescopes?

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  • $\begingroup$ Odd -- I'm pretty comfortable claiming that a geo-synch satellite or two, most likely TV providers ( my old dish pointed at one) are pretty bright right around sunset and again around sunrise. Bright as an inner planet. $\endgroup$ Sep 1 '20 at 14:29
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No, but they are easily seen with a small telescope on a sturdy mount. March and September are the best times. Use an app to help you. My favorite way is to keep M11, the Wild Duck Cluster, in view with a medium power eyepiece. Every few minutes, a "star" will slowly track through the southern edge!

It's a fun and instructive exercise to calculate the declination of an equatorial GEO orbit from a given latitude!

  • GEO satellites can be quite large, and while they are said to be +10 to +14 magnitude they can flare far brighter due to flat surfaces, both solar panels and thermal radiators. From http://www.satobs.org/geosats.html

Typically the satellite will be in the mag. +11 to +14 range (or dimmer), but brightening by several magnitudes when the geometry is favourable (around mag. +5 to +6 is not untypical). One satellite is reported to have briefly been visible to the naked eye at mag. +3!

...I found three other satellites, all between magnitudes 13 and 13.5, each a degree or two from the last! Chances are that one of the satellites is Canada’s Anik C1, although I could not identify it for certain.

From Sky and Telescope's How to See and Photograph Geosynchronous Satellites

Many geosynchronous satellites shine between magnitudes 10–12, so you can spot them in telescopes as small as 4 inches. They're also easy to photograph. High ISOs and fast, low light lenses aren't necessary, just a camera capable of a several-minute-long time exposure — long enough for the stars to trail, so you can easily tell them apart from the satellites. Set your shutter speed to "B" and ISO at 400. You can hold the shutter button down with your finger, but a shutter release cable is much better and vibration-free. Use a 100–200-mm telephoto lens, focus sharply, and expose for 2–4 minutes. When you enlarge the image, you'll should see long trails and a line of pinpoint dots — satellites!

synodic plot of GEO orbits

Shiny surfaces on communications satellite

Shiny surfaces on communications satellite

From How do commercial broadcast satellites in GEO produce such carefully shaped signal footprints? you can see thermal radiators that are highly reflective in the visible (and near IR)

Shiny surfaces on communications satellite

From How will GOES-R simultaneously point some instruments down at Earth and others sunward?

Shiny surfaces on communications satellite

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  • $\begingroup$ not exactly related, but don't forget radio observations! “Mysterious radio signals” - how could a geostationary satellite and Ross-128 line up with Arecibo? $\endgroup$
    – uhoh
    Sep 1 '20 at 8:16
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    $\begingroup$ Brighter than I expected. But then I guess, 100 times further away and 10 magnitudes fainter than low-Earth orbit satellites is about right. $\endgroup$
    – ProfRob
    Sep 1 '20 at 8:28
  • $\begingroup$ @RobJeffries This was (obviously) fun to write ;-) if you (or anyone else) happens to spot one and can estimate a brightness, that would make for an interesting supplemental answer! $\endgroup$
    – uhoh
    Sep 1 '20 at 8:43
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    $\begingroup$ The October 2020 Sky & Telescope magazine has an article about observing them. Since they flare when the apparent declination of the satellite equals the Sun's declination, the flare "season" occurs near the March and September equinox. It has been years since I saw one, and it was through a car windshield, but I think they can easily reach second magnitude under the right conditions (date, time, and satellite design.) $\endgroup$
    – JohnHoltz
    Sep 1 '20 at 16:25
  • $\begingroup$ @JohnHoltz Thanks! Consider adding another answer summarizing what's in that article, or please feel free to edit this answer. $\endgroup$
    – uhoh
    Sep 1 '20 at 16:45
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Geostationary satellites are often seen with telescopes and occasionally result in a "Something Moved! Did I see a UFO?" sort of message.

If you have a tracking telescope aimed at a star in the same field if view of a geostationary satellite the satellite will appear to move against the background. It you turn off telescope tracking the satellite will appear to be stationary but the stars will move against the background.

Geostationary satellites come in various sizes shapes and reflectivity. No doubt the brighter satellites will be visible with binoculars.

Naked eye???

What a wonderful project for an aspiring astronomer. Sharpen up your Google, I will watch for your report.

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