1. Galaxies
Sombrero Galaxy
(spiral)
Andromeda Galaxy
(spiral)

2. Galaxies

3. What is a galaxy?
Stars are not uniformly distributed through the universe but are unevenly clustered into groups.

4. What is a galaxy?
A galaxy is a massive system of stars, dust, and gas held together by gravity.
Galaxies contain billions of stars.

5. What is a galaxy?
Within galaxies, are smaller groups of stars known as star clusters.
A “cluster” is a group of stars inside the galaxy.
M13 Cluster
in our galaxy
can see with binoculars
over 100,000 stars

6. What is a galaxy? Hubble identified three types: Spiral Elliptical
Irregular

7. Spiral Galaxy
Shaped like a flattened disk with a bulging center and “arms” that curve in a spiral pattern
Rich with dust and gases
New stars are in “arms”
Old stars are in the center
(e.g.) Milky Way

8. Elliptical Galaxy
Shaped like a sphere or “egg” because stars are close together near the center & farther apart on the outside edges
Very little dust and gas
Very few new stars
Mostly old stars

9. Irregular Galaxy No definite shape or organization
Contains clouds of dust and gases
Contains a mix of old and new stars

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

11. Milky Way 3 1 2 1 – Closest Milky Way “arm” 2 companion galaxies:
2 - Large Magellanic Cloud
3 - Small Magellanic Cloud

12. Distances between Galaxies
Galaxies are so far away that even the closest galaxies appear as fuzzy patches of light.

13. Distances between Galaxies
Galaxies are grouped together into clusters, which form superclusters.
The Milky Way is part of a cluster called the Local Group.
The farthest galaxies from Earth are about 14 billion light years away.

14. Mind = Blown

15. Big Bang Theory
In the late 1920s, Hubble discovered that most of the galaxies he observed were moving away from Earth.
This could only be explained if the entire universe was expanding.

16. Big Bang Theory
The Big Bang Theory states the expansion of the universe began about 14 billion years ago.
The universe was a tiny point that contained all the energy and matter of the universe.
The universe began to expand rapidly, and cool.

17. Big Bang Theory
The universe was too hot to form elements for several hundred thousand years.
The universe consisted of radiation and subatomic particles.
As the universe cooled, hydrogen and helium atoms formed.

18. Big Bang Theory
Galaxies began forming several hundred million years after the Big Bang.
Clouds of hydrogen and helium possibly became more dense in some regions.

19. Big Bang Theory
The dense regions began to clump and form stars.

20. Dark Matter & Dark Energy
Scientists can calculate how much mass the universe should contain by the way galaxies move through space.
All the matter they can detect added together is less than the amount needed.
The missing matter is called dark matter.
The missing energy needed to explain the expansion of the universe is called dark energy.

21. Which is the shape of the Milky Way? A flat B elliptical C irregular
12.3 Galaxies
Which is the shape of the Milky Way?
A flat
B elliptical
C irregular
D spiral

22. How old is the universe thought to be?
12.3 Galaxies
How old is the universe thought to be?
A several hundred thousand years
B 1 million years
C 14 billion years
D 63,000 million years

23. A cluster is a group of ____. A stars B solar systems C galaxies
D planets

24. The average distance between Earth and the Sun is called a(n) ____.
SCI 4.c
The average distance between Earth and the Sun is called a(n) ____.
A light-year
B astronomical unit
C angstrom
D solar unit

25. SCI 2.g
What causes clouds of gas and dust to form clumps in interstellar space?
A solar winds
B gravity
C electrons
D dark matter

26. Galaxies have what three shapes? A cluster, group, and spiral
SCI 4.a
Galaxies have what three shapes?
A cluster, group, and spiral
B supercluster, cluster, and group
C spiral, elliptical, and irregular
D regular, irregular, and flat

27. Vocab – Galaxies text p. 528-534
galaxy
spiral galaxy
Milky Way
elliptical galaxy
irregular galaxy
randomly
big bang theory
HIGHLIGHT!!!