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I was gazing through my binoculars at Jupiter last night and noticed 3 (maybe 4) tiny dots in line with it. A first I thought they might have been background stars but quickly realised their colour was similar to that of Jupiter and their brightness was larger than expected considering their size. As a result, I'm pretty certain I was looking at Jupiter's moons.

Presumably, I was seeing the largest of its moons (Io, Europa, Ganymede, Callisto). They were far too tiny to see any details, obviously, but would it have been only those moons I could see? I assume the rest are too small. And is seeing those 4 moons as tiny bright dots through my 7x50s feasible?

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  • $\begingroup$ Please do not write last night - edit your question and enter exact time and location. $\endgroup$ – Jan Doggen Mar 8 '16 at 13:41
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The galilean moons are visible in binoculars, indeed. Yesterday evening (assuming you're in the western hemisphere), 3 of them were visible as separate dots. See the chart here:

http://www.wolframalpha.com/input/?i=jupiter+galilean+moons+on+march+6+2016+at+9pm+pst

You can adjust the query to reflect your time zone, and the actual date/time of the observation.

There are also smartphone apps that allow you to determine the position of the moons at any given time. On Android I use the Moons of Jupiter app.

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Yes, you have definitely seen the Galilean moons, as they are named after their discoverer — Io, Europa, Ganymede, and Callisto. Those four moons are so bright that you would in fact be able to see them with the naked eye if they hadn't been just next to the much brighter Jupiter.

In contrast, the fifth brightest Moon, Amalthea, requires a telescope of at least 25 cm diameter.

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