Determine the moons of Jupiter through a telescope
I was doing my own "space exploration" last night with a telescope. Being a space noob I can't visually determine stars or planets (I know the moon, though), but I focused on one particularly bright one when I saw 4 smaller "stars" on each side. After a quick Google I learned I had discovered the moons of Jupiter!
I now know the moons I could see were Io, Europa, Ganymede, and Callisto. But which is which?
Is there an easy way to determine which Galilean moon is which?
Use an orrery that will let you specify a specific epoch and vantage point. There are some quite fancy ones online, for example this Solar System Scope:
What you do in this particular tool is click on the calendar bar below and enter date and time of your observation (if you forgot that, there's a good chance your photograph has a time stamp, either of the file or in its EXIF data). You can adjust epoch later on, too. Then double-click on Jupiter, then its Orbit button, then click on link As seen from Earth below, then click Go back button and use mouse wheel to zoom out so all four Galilean moons display. Then compare with the photograph that you took. Note that it might take a bit of rotation for you image to align perfectly. I use the old neck twisting and turning technique, but photo editing tools or even rotatable screens will do just as well, if not better.
Note that this mentioned tool does offer settings to switch between orrery and realistic model and large and realistic sizes of displayed celestial bodies. But there are many such tools online or downloadable for both computers and smartphones. I think even this one is available as an app for smartphones for free, but last time I tried to install it, it didn't work for me. Maybe they fixed that. Do check because it's a lot easier if you can check orbital alignment of Galilean moons as seen from Earth directly on the field, as you're doing your observations.
Have clear skies and I wish you happy hunting for planets and moons of our Solar system and beyond!