1. Galaxies
PJHS Grade 8 Science –

2. What is the name of our galaxy?
Our goals for learning:
What are the three major types of galaxies and the characteristics of each?
What is the name of our galaxy?
Where is our solar system in our galaxy?

3. What is a galaxy?
A galaxy is a large grouping of stars, gas, and dust in space that are held together by gravity.
The largest galaxies contain more than a trillion stars. Smaller galaxies may have only a few million.
Scientists estimate the number of stars from the size and brightness of the galaxy.

4. Main Types of Galaxies
Spiral
Irregular
Elliptical

5. Properties of Spiral Galaxies
Shaped like flattened disks with one or more spiral arms.
Sketch one!
Our galaxy, Milky Way, is a spiral galaxy.

6. Properties of Elliptical Galaxies
About 1/3 of all galaxies.
Simply massive blobs of stars.
Sketch one!
Round or elliptical in shape.
Contain very little gas or dust.
Because of little gas, no new stars are forming.
The largest and smallest galaxies are elliptical galaxies.

7. Properties of Irregular Galaxies
Do not fit into any other category.
Chaotic mix of stars, gas and dust
Usually found near large spiral galaxies who may be distorting their shape.
Sketch one!

8. Contents of Galaxies
Galaxies are made of stars, planetary systems, gas clouds, and star clusters. Nebulas are giant clouds of gas and dust where stars can form.
Nebula are found in spiral galaxies but not elliptical galaxies.

9. What type of galaxy is this?

10. What type of galaxy is this?

11. And this?

12. What is the name of our galaxy?

13. Who can describe the Milky Way Galaxy?

14. Characteristics of our home, the Milky Way Galaxy
Flattened Disk
Bulge in Middle
Fried Egg
Not solid from edge to edge
Huge
1,000-3,000 Light Years Thick
100,000 Light Years across (Diameter)

15. Where is our solar system in our galaxy?
The Sun and our solar system is located in one of the outer arms (Orion’s Arm) of the galaxy. The distance from the Sun to the center of the galaxy is about 30,000 light years.
All objects in the galaxy revolve around its center.
The sun and our solar system take about 240 million years to make one trip around the center of our galaxy.

17. Milky Way from Earth
Milk

18. Carl Sagan’s Pale Blue Dot

19. Get your Plickers card out!