1. Ch Star Groups

2. 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.

6. 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.

7. Types of Galaxies Spiral Barred spiral
Elliptical---no young stars; little dust and gas
Irregular

12. 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.

14. Star Clusters
Groups of stars, either open clusters (loosely shaped) or globular clusters (spherical shaped).

16. 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.

19. 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.