Download Ch. 27.3 Star Groups

Ch. 27.3 Star Groups
Constellations
Patterns of stars in the sky, in which the
stars are not necessarily close together.
 88 constellations recognized by
astronomers.
 Most don’t look like the figures they are
named after.

Galaxies
Typically contain about 100 billion stars.
 Also contain bright and dark nebulae.
 Our own Milky Way is part of the Local
Group of galaxies.
 Up to a trillion galaxies in the known part
of the universe.

Types of Galaxies
Spiral
 Barred spiral
 Elliptical---no young stars; little dust and
gas
 Irregular

The Milky Way
A spiral galaxy.
 From Earth, seen as a faint cloud-like
band of stars.
 100,000 light-years in diameter.
 2,000 light-years thick in the center.
 One complete rotation in 200 million years.
 Our sun is about 30,000 light-years from
the center.

Star Clusters

Groups of stars, either open clusters
(loosely shaped) or globular clusters
(spherical shaped).
Binary Stars
Most stars in the galaxy are part of double,
or even multiple-star systems.
 Important in determining stellar masses,
by examining gravitational effects.

Formation of the Universe
Big Bang—the theory that the universe
exploded from a singularity 12 to 15 billion
years ago, and has been expanding ever
since.
 Quasars are seen at the most distant parts
of the observable universe; believed to
have formed shortly after universe’s
formation.
