The Moon

Did you know that we always see the same side of the moon? Because of its rotation around the earth, you'd think that we see all parts of it as it orbits around, but the moon is actually a little lopsided so the same part always faces us. There's also no 'dark side' of the moon - different parts of the moon are lit all the time:

Notice how half the moon is always lit (inner circle), but how much gets reflected and viewed from Earth always changes (outer circle). (source)

So that's how much is LIT by the sun and gets reflected to the Earth, but it doesn't really show how we always see the same side. Look at this little gif of all the different moon phases, from a whole month's worth of different moons:

Watch the big splotch in the right hand side - it rotates a little but it's always facing us

Watch this video for a bit more explanation about how the moon's rotational period matches it's revolutionary period:

Watch to the end to see the light changing while the moon rotates

We always see the same side because the moon is kind of egg-shaped - it's a little heavier on the side closer to the earth, so that side always faces us! So what does that other side look like? NASA has a lunar orbiter that goes around the moon and has taken pictures of the other side:

There's some animation in here too, but it's still a good picture of that other side of the moon

I did another post on the tides last year, so if you want to know how those work check that out here.