The Universe
Yours to Discover
Almost all of the light in space comes from stars. In our region of space, known as the Solar System, the Sun emits most of the light, but that's because the Sun is a star and that's what stars do - they emit light!
Stars, including the Sun, emit light because deep down at the core of a star there are nuclear fusion reactions happening. These reactions produce an enormous amount of heat and light. In the Sun, the nuclear fusion reaction turns hydrogen into helium. In about five billion years, when the Sun gets hotter, another nuclear fusion reaction will begin inside the Sun. This reaction will turn helium into carbon and oxygen. In stars that are even bigger (and hotter) than the Sun, there are nuclear reactions that create neon, magnesium, sulfur, silicon, and iron. |
Sun
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Most objects in space, other than stars, reflect light. For example, planets like Venus, Mars, Jupiter, and Saturn all reflect light. You can look up into the night sky and easily see these four planets for yourself, from your backyard, using just your eyes - no telescope required! All four of these planets look like bright stars, but they're not stars because stars emit light and planets only reflect light. The light that you see when you look at these planets is actually sunlight, which has reflected off the surface of the planet. The same is true when you look at the Moon. The Moon is very bright, but all of that light is just reflected light from the Sun.
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Moon
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