Hi Isaiah,

The most of the energy we get from the Sun comes to use in the form of light, and here is a lot of it! We can measure it at the surface of the Earth and also, to get a better idea, up in space above Earth's layer of air.

We think that energy is produced deep inside the Sun by atomic reactions. We can tell from studying the Earth and Moon that the Solar System must be quite old, about 5 billion years. The only power source we know of that can keep the Sun and other stars producing energy for billions of years is nuclear energy. The nuclear energy heats the Sun and eventually is given off from the Sun's surface as intense light.

We can calculate what the surface and inside of the Sun would be like if that were true, and when we make measurements we find out that the Sun fits those predictions pretty well. So, we are pretty sure we are right.

Terry