1. Star Systems & Galaxies

2. Star Systems & Clusters
Most stars are members of groups of two or more stars, called star systems.
Our solar system only has one star.

3. Binary Stars Star systems with two stars are called binary stars.
A eclipsing binary system occurs when one star periodically blocks the light from another star.
Binary stars
eclipsing binary system

4. Star Clusters
Many stars belong to larger groupings called star clusters.
Open clusters have a loose chaotic appearance and are made up of young stars (less than a billion years old).
Globular clusters are round and densely packed groupings containing older stars (12-13 billion years old).
PLIEADES OPEN CLUSTER
47 Tucanae, billion years old, 15,000 light-years from Earth.
Globular Cluster

5. Galaxies
Galaxies are large groups of stars, star systems, star clusters, dust, and gas bound together by gravity.
Come in a variety of shapes and sizes.
Contain trillions of stars.
Classified by shape.
It is estimated that there is over 100 billion galaxies.

6. Three Shapes of Galaxies
Andromeda spiral galaxy
Spiral Galaxies
Flattened arms that spin around the center, mostly made up of young stars.
Elliptical Galaxies
round, from flat disks to spheres, contain older stars.
Irregular Galaxies
Irregular shape, so they make up their own category, generally young stars with lots of dust and gases.
Elliptical Galaxy M87
Irregular Galaxy M82

7. Milky Way Galaxy
Our solar system is located in a spiral galaxy called the Milky Way.

8. Scale of the Universe
Since numbers astronomers use are often very large, they use scientific notation to describe sizes and distances in the universe.
Example: 1 light-year is 9,500,000,000,000,000 meters or 9.5 X 1015 meters.

9. Galaxies, and the Universe

10. The Universe The Universe is made up of many Galaxies.
The study of the origin, structure, and future of the Universe is called Cosmology.
Astronomers use galaxies far away to hypothesize how they form.

11. Doppler Effect
Change in wavelength caused by the apparent motion of the source.
Blue Shift - light from objects coming toward you is compressed looks more blue.
Red Shift - light from objects moving away looks more red.

12. Big Surprise No Galaxies showed blue shift
All galaxies showed red shift.
Which means
All galaxies were moving away
The universe is expanding

13. Origin of the Universe
The theory that the universe began with a tremendous explosion is known as the Big Bang Theory.
13.7 billion years ago, all matter was compressed into one spot and expanded rapidly.
Explained red shift.