Have you ever looked up at the night sky and tried to count the stars? If you have, you probably gave up. With you eyes alone you can see about 3,000 stars, but have you ever wondered what they are? In this lesson, we will try to answer that question.
Stars are large balls of gas that give off light. Stars are made of layers. The outermost layer is made a stream of particles that flows away from the star (called the solar wind), a ring of light (the corona), and a layer of hot gasses (called the photosphere). Scientists don't have a clear idea of what is inside this outer layer, but they think that inside, there are more layers, increasing in temperature and density until the core. The star's nuclear reactions take place inside the core (see How Do Stars Shine?). But there were so many, you probably gave up. Scientists know that you can see about 3,000 stars with your naked eye. With powerful telescopes, scientists can see billions and billions of other stars.