1. Chapter 27 Stars and Galaxies
Section 3
Star Groups
Notes 27-4

2. Constellations Star pattern or regions Stars appear to be close
Stars that make up one constellation are not all the same distance away from the earth
Individual stars in constellation don’t seem to move
Whole constellation do move across the sky from night to night

3. Constellations 88 constellations are recognized
Named for animals (real or imaginary)
Draco (dragon), Ursa Major (great bear)
Named for gods or heroes
Hercules, Orion

4. Constellations
Used to divide the sky into sections like a map of the United States
Use the constellations to find other stars and galaxies
Stars in constellations are labeled according to apparent magnitude
Brightest = Alpha (α)
Second brightest = Beta (β)
Stars can also have names that don’t relate to the constellation at all
Alpha Scorpii is also called Antares

5. Galaxies Large scale groups of stars bound together by gravity
Typically they are 100,000 ly in diameter and have 100 billion stars
Contain nebulae
Can reflect light from nearby stars or produce its own light from hot gases
Some are dark; absorb light from stars behind them

6. Galaxies Nearest galaxies to us (Milky Way)
Large Magellanic Cloud
Small Magellanic Cloud
150,000 ly away
There are 17 other galaxies that are within 3 million ly of the Milky Way
Called the Local Group

7. Galaxies
Spiral:
Has a nucleus of bright stars and flat arms that spiral out from it
Contains young stars, gas and dust
Some have a bar of stars that runs through the center
Called barred spiral galaxies
Milky Way is a spiral galaxy

8. M74 – Spiral Galaxy

9. Galaxies Elliptical: Can be nearly spherical to a flatten disk
Have a very bright center (but no arms)
No young stars
Contains little dust or gas

10. M87 – Elliptical Galaxy Also called Virgo A

11. Galaxies Irregular: Has no particular shape Are smaller and fainter
Believed to have no enough gravity to organize the stars
Could also be from two galaxies colliding
Stars are unevenly distributed

12. IC10 – Irregular Galaxy

13. Milky Way Cloud like band that stretches across the sky Spiral Galaxy
Each star is orbiting around the center
Diameter = 100,000ly
Thickness (center) = 2,000 ly
Sun’s distance from center = 30,000 ly
Revolves 250 km/s
Completes one revolution in about 200 million yrs

14. Milky Way Galaxy

15. Milky Way Star clusters
Globular cluster: spherical shape with many more stars than open clusters
Found at the center of the galaxy
Open cluster: loosely shaped with less stars than globular clusters
Found on the arms of the galaxy

16. Milky Way Binary Stars Multiple star systems
Pair of stars that revolve around each other
Used to determine stellar masses

17. Universe Around 12-15 billion years old
Big Bang occurred that long ago
All matter moved outward
Gravity condensed some matter into galaxies and other masses
Galaxies are still moving away

18. Universe
Quasar: star-like objects that formed 12 billion years ago (12 billion ly away from Earth)
Give off radio and x-rays
Some of the first objects to form after the Big Bang
Evolved into galaxies
Read pg. 565 “Earth Beat”

19. Quasar