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I saw a few days ago two luminous points in the sky, which were quite close (about 1-2 degree of separation between them) and not apparently moving (or to slow to be noticed with the naked eye). The apparent luminosity of these points was close to the one of Jupiter (a bit less maybe, but far more luminous than Saturn).

The luminosities of these points increased a bit and after a few seconds they faded. I guess these were not satellites entering in the shadow of the Earth as they were not moving. And I think that the probability for this to be two meteors falling exactly towards me is quite low...

Any suggestion this might be ?

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    $\begingroup$ Could be an airplane flying toward you with its landing lights on. $\endgroup$
    – Mike G
    Commented Jul 22, 2020 at 16:02
  • $\begingroup$ What was the color of the points? Were they white like most stars? $\endgroup$
    – Ioannes
    Commented Jul 22, 2020 at 16:26
  • $\begingroup$ Were they near Jupiter or much higher or lower? $\endgroup$
    – AstroShannon
    Commented Jul 22, 2020 at 16:37
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    $\begingroup$ Almost certainly distant airplanes. They will be too far for any sound, close to the horizon, very bright (when the headlights point towards you) then suddenly fading to invisible as they turn. They don't appear to move much (because they are heading towards you) The brightness of airplane landing lights is really quite surprising, They could easily be 50km or more away, so you won't hear anything. $\endgroup$
    – James K
    Commented Jul 22, 2020 at 21:27
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    $\begingroup$ I agree about the airplane theory - my answer had mistakes. Tomorrow I'll delete it since it's almost certainly not what you saw, but I wanted you to see why I was deleting it first. $\endgroup$
    – AstroShannon
    Commented Jul 23, 2020 at 4:16

2 Answers 2

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Edit 1: @JohnHoltz correctly pointed out two errors - geosats are on the equator, not ecliptic. My brain was thinking "equator" but my fingers had other plans. I read about geosat flares quite some time ago and thought it was solstices when they could be seen but it's around equinoxes, not solstices. I've changed my mind and think planes are the most likely answer as to what was seen. However, I do stand by the statement that geosat flares end due to the Earth's shadow. They are unlike other sat flares in this regard according to CalSky which I've always trusted above all other sources for info like this. The link is in the first sentence of my original post below. End of edit.

Edit 2: (by @uhoh) answers to How bright are geostationary satellites due to reflected sunlight? explain that flares from GEO can be bright enough to be visible, and when you look at how big those "mirrors" are it's not hard to imagine!

The heat radiators are dark in thermal IR but mirror-like in the visible to prevent absorbing heat from sunlight. The solar panels are larger but have fairly low reflectivity.

I'm 90% sure that you saw geostationary satellites catching the Sun just right causing a flare. It's the right time of the year for them to be seen, too. Jupiter is sitting on the ecliptic at the moment which is where geosats are parked in clusters (the reason there were two dots visible at 1-2 degrees in separation). Their brightness increased because they were moving towards opposition (reflecting more sunlight), then faded because of the Earth's shadow exactly as you thought. Geosats move slowly against the background stars since their job is to remain over the same point on the Earth; this is how people can get satellite TV with satellite dishes on their rooftops pointing at the same spot all the time. It'd be hard to notice their motion without keeping a steady eye on them for 15 mins or so.

Your description matches perfectly with a geosat flare and I'm a bit jealous because I haven't caught one yet! Congratulations, you witnessed an event that isn't often visible to the naked eye! They show up in my astropics all the time, but I have yet to see one with only my eyes.

A comment on the video in the link: Geosats stay in the same position over the Earth but this video makes them appear to be moving left as the stars set behind them. I was puzzled by this until I realized the ground objects visible in the bottom of the video are slowly moving, so the time lapse video was made with a camera slowly panning the to the right. The video shows the clusters well but with the wide angle the individual geosats in each cluster aren't visible. I think the ones you saw were in the same grouping.

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    $\begingroup$ Geosats are not near the ecliptic. They are near the equator. At my latitude of 40 north the geosat belt is near -6.5 declination. I do not know what it would be from Paris but not farther south than Jupiter. Also, geosats do not go into the Earth's shadow at this time of year. Only about 1 month centered on the equinox. The flare season is also around the equinox based on my experience. $\endgroup$
    – JohnHoltz
    Commented Jul 22, 2020 at 22:37
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    $\begingroup$ @JohnHoltz You are correct, thank you for catching my typo. My brain was saying equator but my fingers didn't care. I suspect you're also correct about the lights being planes as well. From southern France, it looks like geosats are around -7 deg dec... while Jupiter is a lot lower at -22. I'll delete my post; I see so many geosats in my astro images they jump to my mind more quickly than they should. I do stand behind my statement that geosat flares end in the Earth's shadow, though. Iridium flares, as well as other low earth orbit flares, have nothing to do with the shadow but geosats do. $\endgroup$
    – AstroShannon
    Commented Jul 23, 2020 at 3:52
  • $\begingroup$ Being new to Stack Exchange, I'm a little unclear on when I should delete my answer or edit it as I did. I think @JohnHoltz is correct. $\endgroup$
    – AstroShannon
    Commented Jul 23, 2020 at 4:11
  • $\begingroup$ I am still quite sure it were not airplanes, this flare explanation match more with what I saw. This was clearely souther than the ecliptic so it could match with these satellites ? Maybe if it is not possible this were a geostationnary satellite, could it be another type of satellites (still at a very high altitude, as it was not moving on naked eye observations) ? $\endgroup$
    – Lexi Jones
    Commented Jul 24, 2020 at 14:51
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    $\begingroup$ @LexiJones There are so many sats with such a wide range of orbits it's hard to say which kind it might have been. Some sats orbit higher than geosats (distance from Earth) and have parts of their orbit where they're moving slowly (against the background stars) that they can look stationary. Plus, there are a surprising number of sats which are no longer working and their orbits have changed dramatically. If you have a lot of sky watching experience and feel confident you can tell the difference between planes coming towards you (which can look stationary) then I'd say you saw a sat flares. $\endgroup$
    – AstroShannon
    Commented Jul 24, 2020 at 20:01
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I think James K is right, it might have been airplanes. It happened to me a few times that I saw one very bright yellowish and even brighter getting dot kind of in front of me, and as it came close enough I recognized it's blinking and an airplane. When airplanes are far enough and about in front of you, there is no blinking and they look like big yellowish dots and you might even think it's a meteor flying towards you. And you saw even two airplanes flying towards you. It's possible that they look like disappearing when they turn before coming close enough.

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