Sunlight contains many different colors. Normally, we see all the colors mixed together as white light. We see a rainbow when sunlight separates into bands of different colors. These bands of red, orange, yellow, green, blue, indigo, and violet light are also known as the visible spectrum.

A rainbow is created when sunlight passes through raindrops. Light travels through different substances at different speeds. When light travels through water, it slows down. The reduced speed causes light to bend or refract.

To understand how a rainbow is made, it is helpful to understand how a prism works. A prism is a triangular shaped piece of glass. The path of a light beam changes as it goes through a prism. Glass slows the speed of light. When light travels through a prism, it is refracted once while going in and again as it passes through. The refraction separates white light into its many colors.

A water drop acts like a prism. Light refracts as it enters and leaves a drop of water. The refracting light is separated into the colors of the spectrum. When the sky is filled with drops of water, a rainbow is created. Light that enters the drops is refracted. Refraction makes each color visible in its own band. Each color of the spectrum has a slightly different wavelength. The different wavelengths bend in slightly different ways. Long wavelengths bend the least, while short wavelengths refract the most. Red light has the longest wavelength and violet light has the shortest. The other colors have wavelengths that fall between. Because color refraction is consistent, the colors of the rainbow or any other spectrum look the same and appear in the same order. We use the memory device ROYGBV (Roy G. Biv) to signify the order of colors.

The combination of all the separated colors creates the beautiful arching rainbow. Since light needs to pass through the raindrops, rainbows are always seen in the part of the sky opposite the Sun.

We see the colors of a typical rainbow as light comes from our Sun. Any star similar to our Sun would create a rainbow with the same colors. Light from different types of stars would create different colored rainbows, some that we couldn't even see with our eyes. Astronomers study how a star's light separates. This separation is called the star's spectrum.

NASA astronomers study spectra to learn more about a star's characteristics. The colors tell astronomers what gases make up the star. When we see a spectrum identical to the Sun's, we know that the star has similar elements to our Sun. Hydrogen and helium are the most abundant gases in all stars, but small amounts of other elements give each star its unique color spectrum.

It is difficult to study stars from Earth because Earth's atmosphere filters out many of the spectra's waves. To avoid this problem, NASA has placed satellites and telescopes in space. Using satellites and space telescopes above Earth's atmosphere, NASA has learned many new things about stars. Someday, maybe you will become an astronomer and use similar tools to study stars.