Day, Night, and the Sky: Our Sun and Moon

Have you ever wondered why the sky is bright in the morning but dark at night? Or why the Moon sometimes looks like a full circle and sometimes like a thin slice? You haven't moved from your planet — so what is going on up there? Think about what you already know about the Sun and the Moon before we dive in.

**The Sun: our nearest star** The Sun is a huge ball of hot, glowing gas. It is so big that about one million Earths could fit inside it. The Sun gives off light and heat. That light travels through space and reaches Earth, which is why daytime is warm and bright. **Why do we have day and night?** Earth is always spinning, like a slow top. It takes 24 hours — one full day — to spin all the way around once. When your part of Earth faces the Sun, it is daytime and the sky is light. When your part spins away from the Sun, it is night-time and the sky is dark. The Sun has not gone anywhere — you just can't see it from where you are. **The Moon: Earth's companion** The Moon is a large ball of rock that travels around Earth. It does not make its own light. Instead, sunlight bounces off the Moon's surface and reaches our eyes — a bit like a mirror. This is why the Moon can look so bright in a dark sky. **Why does the Moon's shape seem to change?** As the Moon travels around Earth over about 28 days, we see different amounts of its sunlit side. Sometimes we see all of it — a full moon. Sometimes we see only a thin curved slice — a crescent. These changing shapes are called the phases of the Moon. The Moon itself has not changed shape; we are just seeing more or less of its lit side.