What is dayside?

The dayside is the part of something that faces the light, just like when you're outside playing on a sunny day.

Imagine you have a round ball, like a soccer ball. If you put it in the sunlight, one half of it will be bright and visible, that’s the dayside. The other half, which is facing away from the sun, will be darker, we could call that the "nightside."

Now think about Earth. When it spins around, some parts of the planet are facing the Sun, those places have sunlight, so they're on the dayside. People there can play, read books, or even take a nap in the sun!

Later, when Earth turns, the same spot might be on the "nightside", no sunlight, so it's time for bedtime.

So the dayside is simply the part of something that’s lit up by the Sun. Just like your face when you're sitting in front of a lamp!