Stars form within cold, dark clouds of gas and dust scattered throughout the galaxy. The space between stars is filled with a thin, interstellar gas and dust that forms nebulae. Emission nebulae emit their own light and are found near hot, luminous O and B type stars, while dark nebulae are opaque and block light from stars behind them.

1. Investigating Astronomy
Timothy F. Slater, Roger A. Freeman
Chapter 11
Inferring Patterns in
Star Life Cycles

2. Star Formation
• Observations across the sky
reveal that stars form within
cold, dark clouds of gas and
dust that are scattered
abundantly throughout our
galaxy.
• Like the mythical phoenix,
all new stars arise from the
ashes of the old.

3. Interstellar Gas and Dust
• The space between the stars is NOT vacant, but filled with
a thin gas laced with microscopic dust particles: the
interstellar medium.
• Clouds of interstellar medium are known as nebula (plural
nebulae).

4. Emission Nebulae
• An emission nebula
emits its own light,
with the characteristic
emission spectra
similar to that of a hot,
thin gas.
• Emission nebulae are
found near hot,
luminous stars of
spectral types O and B.

5. Dark Nebulae
• A dark nebula is so opaque that it blocks any visible light coming
from stars that lie behind it.
• Some astronomers call this nebula “The Cosmic Gecko”