Chapter 28 Stars and the Universe

722 CHAPTER 28: STARS AND THE UNIVERSE
Source of
White Light
Spectroscope
Glass
Prism
The spectroscope is one of the most important tools that astronomers
use. This instrument separates light into its component
colors (wavelengths), like the glass prism shown in
Figure 28-6. When starlight is passed through a spectroscope,
dark lines appear in certain parts of the spectrum. These
dark lines are produced when certain wavelengths of light
are absorbed by gaseous elements within the outer parts of
the star.
Each element has its own characteristic absorption lines.
Since stars are composed primarily of hydrogen and helium,
white light that passes through these elements shows dark
lines in the orange, yellow, green, and blue colors that characterize
hydrogen and helium. These spectral lines correspond
to the energy that electrons absorb when they move to
higher energy levels within the atoms. The atoms give off the
same colors when the electrons fall to lower or inner energy
levels. Each element has a unique set of energy levels. Therefore,
these “spectral fingerprints” allow astronomers to identify
the composition of distant stars.
ACTIVITY 28-4 MAKING A SPECTRUM
Long Wavelengths
Red
Orange
Yellow
Green
Blue
Violet
Short Wavelengths
Figure 28-6 When white
light passes through a glass
prism, the light separates into
the spectrum of colors, or
wavelengths, of which it is
composed.
You can separate sunlight into its spectrum with a glass prism. This
works best in a darkened room where windows face the sun.
Close the shades so that a narrow slit of direct sunlight enters the
room. Place the prism near the narrow opening that admits sunlight.
The prism will bend the light beam and separate it into its