In astronomy, virtually all of the information that we can learn about the Universe comes from various forms of light. Since planets, stars, and other objects in space are so far away and our ability to travel in space is rudimentary, we must glean as much information as possible from their light. Therefore, it behooves you to understand how light works and what kind of information it carries.

A great deal of the information in light from astronomical objects can be derived from the spectrum of that light. You can read about astronomical spectra in the first section of this chapter, and the later sections discuss some of the techniques astronomers use to interpret spectra.

Light and spectrum fundamentals

The most fundamental property that distinguishes one type of light from another is its color. This section introduces the concept of a spectrum as a graphical presentation of the brightness of different colors in light, and you'll learn how to translate between various quantitative properties associated with the color of light. Light behaves both as waves and particles, and you'll see how the properties related to color can be used to describe both the electromagnetic-wave and the photon-particle aspects of light. If you'd like to understand why light is called an electromagnetic wave and exactly what's doing the waving in light, you can find additional resources about the nature of light on the book's website.