Galaxies Grade 10

1. CHAPTER 3
10TH GRADE SCIENCE

3. WHAT IS A GALAXY?
A galaxy (from the Greek word galaxias, meaning
“milky”) is a much larger gravitationally bound
system that consist of hundreds of billions of stars,
gas, dust, stellar matter, and stellar remnants.

4. How big are galaxies?
The largest galaxies have more than a TRILLION
stars.
There are BILLIONS of galaxies in the universe.

5. Galaxies
• The sun is a star in
the Milky Way
galaxy.
• The sun and its
planets are located
about 2/3 of the
way from the
center of the galaxy

7. Components of Galaxies
• Nucleus- the bright
center of the galaxy
• Central bulge- a
spherical-shaped
structure that
usually consist of
old stars, gas, and
dust

8. Components of Galaxies
• Disk- a large, flat
arrangement of young
stars, gas and dust that
surrounds the bulge.
• Halo- a huge, spherical-
shaped structure of
individual or cluster of
old stars surrounds the
disk
• Spiral arms- curved
extensions that stretch
from the nucleus or
bulge.

9. As you look at this image, you will notice many
different types of galaxies. Edwin Hubble, the astronomer for
whom the Hubble Space Telescope is named, began to
classify galaxies in the 1920s, mostly by their shapes. We still
use the galaxy names that Hubble originally assigned.
3 Types of Galaxies

11. Spiral Galaxies
Spiral galaxies appear to have a bulge in the middle and
arms that spiral outward, like pinwheels. The spiral
arms contain many bright, young stars as well as dust
and gas. Relatively few
new stars are forming in the
central bulge.

12. Spiral Galaxies
Spiral galaxies have a bar shaped band
stars that runs through the center bulge
and merges with the spiral arms. These
galaxies are called barred spiral galaxies.
The milky way is
a spiral galaxy

13. The Milky Way

14. The Milky way Galaxy
• The milky way is a barred spiral galaxy with
a large disk that consist of about 100 billion
stars and stretches to about 100 000 light
years.
It has four major spiral Arms
• Centaurus arms
• Norma arms
• Perseus arms
• Sagittarius arms

16. Elliptical Galaxies
• Have a spherical to cigar-
liked shapes with a large
bulge center and a halo.
• They lack a disk and
spiral arms but have large
range size that can be up
to million light-years in
diameter.

17. Elliptical Galaxies
• About one third of all galaxies are
simply massive blobs of stars.
• Elliptical galaxies have very bright
centers and very little dust and gas.
Because there is so little gas, there
are no new stars forming, and
therefore elliptical galaxies contain
only old stars.
• Elliptical galaxies are believed to
have formed from the collision of
many smaller galaxies.

18. Irregular Galaxies
When Hubble first classified galaxies, he had a group of leftovers. He
named them “irregulars.” Irregular galaxies are galaxies that do not fit into
any other class. As their name suggests, their shape is irregular.

19. Can you find examples of spiral,
elliptical, and irregular galaxies?

20. Edwin Hubble
• Classified galaxies by their shape
• He is who the Hubble Space Telescope (a
REALLY powerful telescope used by NASA) is
named after!

21. In your notes, draw each type of galaxy

31. Home work
• Follow Up page 62