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Today at about 18:00 I was looking for Venus near the moon and I saw a short bright line. I thought that maybe I was seeing Venus' crescent but it was perpendicular to the crescent of the moon. I then noticed Venus very close to the moon and realised that the line is Jupiter. I can confirm the location was Jupiter in Stellarium, and I can confirm in Stellarium that the moons are in fact aligned in the direction that I saw the line. Is it possible that I caught a glimpse of the Jupiter-moons system as a line and not a point source?

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Only if your eyes are a heck of a lot better than mine. But see en.wikipedia.org/wiki/Galilean_moons#Visibility –  Keith Thompson Jan 26 '12 at 21:29
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up vote 8 down vote accepted

Maybe.

The Galilean moons are (barely) bright enough to be seen with the naked eye, but they're so close to the much brighter Jupiter that seeing them is at best very difficult (but easy with even low-powered binoculars). Jupiter is not currently at opposition (the closest it gets to Earth), so that's not ideal.

I've never seen them without binoculars or a telescope, but someone with very good eyes in excellent seeing conditions might be able to make them out. And the OP didn't see them individually, just "a bright line".

Try again if you get another opportunity. If you see the "bright line", try rotating your head. If the line rotates along with your head, you're seeing some other phenomenon, perhaps an irregularity in your eyes, or a reflection in your glasses or contact lenses if you wear them. If it doesn't rotate, I'd say there's a good chance you're really seeing the Galilean moons.

Another test would be to repeat the observation when all the moons are on the same side of Jupiter.

Just to gauge your eyesight, how many Pleiades are you able to see without binoculars or a telescope?

(And in case anyone is wondering, Jupiter's rings are not visible with the naked eye; they weren't even discovered until the Voyager 1 flyby in 1979.)

References:

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Thank you. Even before I read this comment, I took my daughters out today at 17:00 and sure enough, when the clouds parted my five year old, myself, and a 9 year old neighbour were able to see Jupiter as a line. The moons are in a completely different configuration now, but it is a phenomenon that is reproducible. The 9 year old described the angle of the line exactly as I saw it, which corroborates with Stellarium's angle for the moons. My own eyesight is not perfect, slightly nearsighted, and I can make out maybe 5 or some individual points of light in the Pleiades. –  dotancohen Jan 27 '12 at 19:50
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@dotancohen: No offense, but I'm still a bit skeptical, given that three different people were able to see them, that your own eyesight doesn't appear to be remarkably good, and that (depending on your location) the sky shouldn't be all that dark at 17:00, and there were some clouds in the sky. Were you in an extremely dark location? Did you try tilting your head? Do you see the line as asymmetric, and if so does the asymmetry correspond to the actual positions of the moons? You make a somewhat remarkable statement, and it's worth being very sure. –  Keith Thompson Jan 28 '12 at 3:45
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I am as sceptical as you are! The location was not extremely dark, however myself and my daughters often try to find Jupiter and Venus during those hours. I did succeed a few weeks ago to see Venus at 16:25 and we have seen Venus at 17:00 quite a few times already. That part I am sure about! But this line is hard for me to believe. The older neighbour certainly see it in the same direction as I see it, and tilting the head confirms that it is not an ocular phenomenon. The only explanation that satisfies me is that we are seeing them blurred together, not individual points of light. –  dotancohen Jan 28 '12 at 9:08
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I don't think so - Jupiter itself is easily visible to the naked eye, but the moons aren't.

Not sure what you would have seen though.

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Did you read @Keith's comment: 'Only if your eyes are a heck of a lot better than mine. But see en.wikipedia.org/wiki/Galilean_moons#Visibility';. To me it looks like he may possibly have seen the moons if he has excellent eye sight and a good seeing condition. –  FrankH Jan 27 '12 at 1:43
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protected by Qmechanic Mar 19 at 14:56

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