Noctilucent cloud

Okay kiddo, have you ever looked up at the sky at night and seen some bright, glowing clouds that look like they're shining? Those are called "noctilucent clouds." They're special because they only show up in the summertime, high up in the sky where it's really cold.

Noctilucent clouds are made of tiny ice crystals that are way up in the atmosphere, about 50 miles above the ground. There's not much air up there, so it's really cold (like, way colder than your freezer!). But even though it's so cold, there's a really thin layer of gas called "hydroxyl" that can react with the water vapor in the air and make these ice crystals form.

Since the ice crystals are so high up, they catch the light from the sun even after it's gone down below the horizon. That's why they glimmer and shine even in the dark of night. They're like little mirrors that reflect the sunlight up to us!

Noctilucent clouds are also really important because they can tell scientists about the Earth's atmosphere. By studying when and where these clouds show up, scientists can learn more about how the Earth's climate is changing and what's happening way up high in the sky.

So that's the big secret to noctilucent clouds -- just a bunch of tiny ice crystals way up high making the sky shine!