Let's start with what the sun is. The sun is a star at the center of our solar system. It is a yellow dwarf, a medium-size kind of star. It is about 100 times wider than Earth. It would take 1.3 million Earths to fill it. Its gravity holds the solar system together. The sun is a huge ball of gas, mostly hydrogen and helium. You could not stand on its surface, because it is not a solid ball. Deep in its core, nuclear fusion turns hydrogen into helium. This makes the sun's energy.

Now let's look at the outside of the sun. The part of the sun commonly called its surface is the photosphere. It is about 10,000 degrees Fahrenheit. That is about 5,500 degrees Celsius. Sunspots are dark, cooler spots on the sun. Their number goes up and down in a cycle of about 11 years. The sun also has an atmosphere. It is made of two layers, the chromosphere and the corona. You might think the surface is the hottest place. In fact, the corona, the outer part of the atmosphere, is much hotter than the surface.

The sun's energy travels to Earth at the speed of light as electromagnetic radiation. The sun is about 93 million miles from Earth. That is very far. Its light takes about 8 minutes to get here. Besides light, the sun gives off heat, and its light and heat warm Earth and make life possible. Never look directly at the sun without special eye protection made for looking at the sun. Think about all of that. Nothing could live on the sun, but its energy is vital for most life on Earth.

The sun also sends out a steady stream of charged particles. We call it the solar wind. It fills the heliosphere, a huge bubble of charged particles around the solar system. Solar storms and fast solar wind can cause a geomagnetic storm. That is a disturbance in Earth's magnetic field. Auroras happen when charged particles collide with the upper atmosphere of Earth. So the sun's reach goes far past Earth, out into space, and it is a very long way.

Words to know

• photosphere: the sun's surface
• sunspots: cooler dark spots
• corona: outer atmosphere
• geomagnetic: Earth's magnetic field