1. The Universe and Galaxies
Glencoe Ch.26 Sec. 3:
pages

2. Astronomy
The study of objects and matter outside the Earth’s atmosphere and of their physical and chemical properties.

3. I. What is the universe?
universe - sum of all matter and energy that ever has, does, and ever will exist
everything physical that exists in space and time
- cosmology – the study of how the universe began, what it is made of and how it continues to evolve and change

4. - Of what is the universe made / composed?
stars, planets, rocks, comets, asteroids, dark matter, dark energy

5. - Of what is the universe made / composed?
- Dark matter – theoretical unseen and undetectable mass that adds to the gravity of a galaxy
- Dark energy – theoretical energy that might be causing accelerated expansion of the universe

6. Most things we see in space are stars
- stars - huge balls of hot gases that emits light
- stars are grouped together by the millions and billions into galaxies

7. A. Astronomical distance
- measured in light years (ly)  a distance measurement
- light year - the distance light travels in one year
 1 light year = 9.5x1015m
 light travels at 3.0x108m/s

8. B. Seeing the past
- time is required for light to travel through space
- light travels a little over 8 minutes from the sun to earth
- the farther away an object/star is, the longer it takes for light to get to us, and the older the light is when it gets to us = “Light is OLD”
- we see the past of other stars in the night sky

9. II. Galaxies
- galaxy - grouping of millions or billions of stars, and dust and gas held together by gravity
there are an estimated 100 billion galaxies in the universe
A. 3 Types of Galaxies - classified by shape

10. II. Galaxies Spiral - disk shaped with spiral arms of dust and gas
- dust and gas provide a place for new
stars to form
- young stars are
bluish in color 
gives spiral
galaxies a blue tint
- looks like a pin wheel

11. Spiral Galaxies

12. II. Galaxies 2. Elliptical  most common type of galaxy
spherical and egg shaped
 NO spiral arms,
little dust and gas
generally have older
stars (reddish in color)

13. Elliptical Galaxy

14. II. Galaxies - Range of sizes
a. Giant - trillions of stars, millions of light years in diameter
b. Dwarf - millions of stars, thousands of light years in diameter

15. II. Galaxies 3. Irregular  least common type of galaxy
- NO well defined shape or structure
some have little
dust or gas, some
have lots of dust
and gas

16. Irregular Galaxies

17. B. Milky Way galaxy - the galaxy we live in
- consists of stars, and, clouds of dust and gas between stars (interstellar matter)
- all the stars we see at night are in the Milky Way galaxy (about 400 billion stars)

18. Milky Way Galaxy – side view
a huge spiraling disk of stars and interstellar matter  1000 l.y. thick

19. Milky Way Galaxy – overhead view
- A huge bulge in
the center
 10,000 l.y. thick

20. Where Are We In The Galaxy?
Our solar system
is about halfway
between the
center and the
edge of the
galaxy (26,000
light years from
the center)

21. B. Milky Way galaxy the nearest galaxy to ours is the Andromeda
galaxy  2.6 million l.y. away

22. C. Gravity holds galaxies together
- dust and gases and stars are attracted to each other by gravity
galaxies are grouped
into clusters  group
of galaxies bound
together by gravity

23. C. Gravity holds galaxies together
- Milky Way and Andromeda galaxies are in a cluster of ~45 galaxies called the “Local Group”
Superclusters - have
thousands of galaxies
 largest structure
in the universe

24. Distances in Space