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Question: How do stars get their light?
Answer: This is actually a very deep question, and to answer it we need to start deep inside the stars. But first we need to know something about light.
Light is energy. More exactly, it is electromagnetic energy. It has many forms and scientists organize these forms of light into something called the light spectrum, or electromagnetic spectrum. Only one small part of this spectrum is light that we can see. This is called visible light. Visible light consists of the colors of the rainbow (red, orange, yellow, green, blue, and violet). You may have heard about the other parts of the electromagnetic spectrum. These are radio, infrared, ultraviolet, x-ray, and gamma ray. Visible fits between infrared and ultraviolet. Our eyes can see only the visible part of the spectrum.
We also need to know how light is made. We will talk about two ways to make light. Atoms, the small particles from which everything is made, can store energy. If we add energy to an atom, it has more than it needs. It will give up this extra energy in the form of light, which is sometimes visible light.
A second way is called fusion. Sometimes conditions exist (very high temperature and pressure) so that small atoms can come together to form a larger atom. When fusion takes place, the new, larger atom (actually the center of the larger atom called the nucleus) has more energy than it needs and gives up some in the form of light.
Both of these light-making processes take place in stars. Let's consider a typical star similar to our Sun. First, fusion takes place in the core (center, very hot part) of the star. The light energy given off by the fusion is gamma light. Gamma has the most energy and as it leaves the core it bumps into the particles (nuclei of atoms and charged particles like electrons, for example) that make up the rest of the star.
Then the light behaves like a bouncing a ball. If you throw the ball to the ground and let it bounce, each time it bounces it loses some energy and does not rise as high. Each time the light bumps into a particle, it gives up some energy to the particle and changes to x-ray and then ultraviolet light.
The ultraviolet light makes its way to the upper layers of the star and adds most of its energy to these layers (called the photosphere) and the atoms with extra energy in these layers produce visible light. This is like putting a piece of iron in a charcoal fire. The hot charcoal is like the ultraviolet light, it is a source of energy. If you put a piece of iron in the charcoal, the iron absorbs the energy from the charcoal and when it gets hot enough, it glows. This is visible light.
Light is produced in other parts of the star called the chromosphere and corona (middle and outer atmosphere of the star), but most of the visible light is produced in the photosphere, the disk that we see. This is one of the reasons the star's (and our Sun's) disk appears bright.
To sum it up, energy stored in atoms is released in the core of the star through the fusion process. This energy makes its way through the star to the upper layers where it adds energy to the atoms. These atoms release the extra energy in the form of light that we can see. Thank you for your question.
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