122

Clouds of gas 170,000

light-years away glow in

this false-color image.

Red represents sulfur

atoms, green hydrogen,

and blue oxygen. Clues

hidden in the starlight

tell a story of star birth

and star death. (NASA, ESA,

and M. Livio, STScI)

Atoms and Starlight

7

Guidepost

In the last chapter, you read how telescopes gather starlight and how spectrographs

spread out the light into spectra. Now you are ready to see what all the fuss is about.

Here you will fi nd answers to four essential questions:

What is an atom?

How do atoms interact with light?

What kinds of spectra do you see when you look at celestial objects?

What can you learn from a star’s spectrum?

This chapter marks a change in the way you will look at nature. Up to this point, you

have been thinking about what you can see with your eyes alone or aided by telescopes.

In this chapter, you will begin using modern astrophysics to search out secrets that lie

beyond what you can see.

The analysis of spectra is a powerful technique, and in the chapters that follow, you

will use spectra to study stars, galaxies, and planets.