Io, a moon of Jupiter, has a synchronous rotation, meaning it takes the same amount of time to rotate once on its axis as it does to orbit Jupiter. This results in one side of Io always facing Jupiter.

Therefore, Io experiences a very long day and night, each lasting about 1.77 Earth days.

Here's a breakdown:

* Orbital period of Io around Jupiter: 1.77 Earth days

* Rotational period of Io: 1.77 Earth days

So, one side of Io experiences constant daylight for 1.77 Earth days, while the other side experiences constant darkness for the same duration.