1. Notes 30.3 Star Groups
Std 2a: Know that the solar system is located in the outer edge of the disc-shaped Milky Way galaxy
Std 2b: Know galaxies are made of billions of stars and comprise most of the visible mass of the universe
Objective 1: Describe the characteristics that identify a constellation
Objective 2: Describe the three main types of galaxies
Objective 3: Explain how a quasar differs from a typical galaxy

2. Star Groups There are trillions of stars in the universe.
Most stars seen from Earth are within 100 light-years from Earth

3. Constellations
Star groups that form patterns can be identified by using a star chart
The sky has been divided into 88 regions
Describes the locations of celestial objects
Constellation - a group of stars organized in a recognizable pattern

4. Dividing up the Sky
The constellations are used to locate particular stars
The stars in a constellation appear close together when viewed from Earth, but they are very far from each other

5. Naming Constellations
Many names come from Latin
Real animals Ursa Major (Great Bear) or imaginary animals Draco(Dragon)
Ancient or Legendary heroes (Orion’s belt)

6. Objective 1: Describe the characteristics that identify a constellation
How many regional division of the sky exist?
88 Divisions
What is group of stars organized into patterns?
Constellation
What language was used to name many constellations?
Latin
What are 2 other ways constellations are named?
Animals or legends/heroes

7. Multiple-Star System
When two or more stars are closely associated, they form multiple-star systems
Binary Stars - pairs of stars that revolve around each other and held together by gravity
Multiple-star systems sometimes have more than two stars
Astronomers estimate that more than half of all observed stars are part of a multiple star system

8. Star Clusters
Nebulas collapse to form groups of 100’s to 1,000’s of stars called clusters
There are Global clusters and Open clusters

9. Galaxies
A large-scale group of stars, gas, and dust that is bound together by gravity is called a galaxy
The Milky Way Galaxy (which we live), has a diameter of about 100,000 light years and more than 200 billion stars
There are hundreds to billions of galaxies

10. Distance to Galaxies
Scientists look at certain stars absolute and apparent magnitude to determine distance to the galaxy
Galaxies are classified by shape
Spiral galaxies
Elliptical galaxies
Irregular galaxies

11. 1) Spiral Galaxies
They have a nucleus of bright stars and flattened arms that spiral around the nucleus
Some have a straight bar of stars that run through the center these are called barred spiral galaxies

12. 2) Elliptical Galaxies They vary in shape from spherical to elongated
They are extremely bright in the center and do not have spiral arms

13. 3) Irregular Galaxies They have no particular shape
Have low total masses and rich in dust and gas
Rarest type of galaxy

14. Objective 2: Describe the three main types of galaxies
What is a large-scale group of stars, gas, and dust that is bound together by gravity?
galaxy
What are the 3 types of galaxies?
Spiral, elliptical and irregular
Which galaxy is very bright and does not have arms?
Elliptical
Which galaxy is the rarest type?
Irregular

15. The Milky Way
A Spiral Galaxy in which the sun is one of hundreds of billions of stars
the name comes from the cloudlike “milky” appearance
it takes the sun about 225 million years to orbit around the galaxy

16. Quasars
Quasar is a shortened term for quasi-stellar (“similar to star”) radio source
Bright, old and most distant objects in the universe
They are related to galaxies not stars
They are at the center of young galaxies, causing their centers to be very bright
Associated with giant black holes in the center

17. Objective 3: Explain how a quasar differs from a typical galaxy
What is a quasar?
Quasi-stellar radio source
Where are quasars found?
Young galaxies
What are they related to?
Galaxies not stars!
What is commonly associated with a quasar?
giant black hole