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ASTRONOMY

14 The Universe
14

This is a planetary nebula in the constellation Aquarius. Planetary nebulae
are clouds of ionized gases with no relationship to any planet. They
were named long ago, when they appeared similar to the planets
Neptune and Uranus when viewed through early telescopes.

CORE CONCEPT

The night sky is filled with billions of stars,
and the Sun is an ordinary star with an average brightness.

OUTLINE

14.1 The Night Sky
Origin of Stars 14.2 Stars
Stars are very large accumulations Origin of Stars Brightness of Stars
of gases that release energy from Brightness of Stars The brightness of a star varies
Star Temperature
nuclear fusion reactions.
Star Types with the amount of light
The Life of a Star produced, the size of the star,
Protostar Stage and the distance to the star. The
Star Temperature Main Sequence Stage brightness you see is compared
Stars appear to be different Red Giant Stage to an apparent magnitude scale
colors because they have Back Toward Main Sequence of brightness.
different temperatures. Beginning of the End for Less Massive Stars
Science and Society: Light Pollution
Beginning of the End for Massive Stars
14.3 Galaxies Star Types
Galaxies The Milky Way Galaxy The Hertzsprung-Russell diagram
Stars are organized in galaxies, Other Galaxies is a plot of temperature versus
the basic unit of the universe. A Closer Look: Extraterrestrials? brightness of stars.
The Life of a Galaxy
A Closer Look: Redshift and Hubble’s Law
A Closer Look: Dark Energy
A Closer Look: Dark Matter
People Behind the Science:
Jocelyn (Susan) Bell Burnell

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