15. Our galaxy A. The Milky Way. B. Spiral shape with armsC. Made up of billions of stars

Our Sun just being one of them.

We have used hydrogen atoms to help us figure out what the Milky Way looks like. We know it is a

spiral, with a center and several “arms.” The Sun is on the Orion Arm, 28,000 light years from the center.

The Sun and the Solar System orbit around the Milky Way.

D. Oldest stars – Found at the center of spiral (bulge and halo)

E. Youngest stars – Found on spiral arms The arms have new stars are forming.

16. Types of GalaxiesA. Spiral - flat, disk shaped, with spiral

arms coming off There are two kinds: normal and barred.

16. Types of GalaxiesB. Elliptical – like an oval, not flat

They range from sphere shaped tofootball shaped.

16. Types of GalaxiesC. Irregular - shaped like none of

theabove.

Galaxies can be bigger or smaller than our own Milky Way!

In 1924, Edwin Hubble discovered variable stars in the Andromeda constellation. He used these

stars to prove that Andromeda was extremely far away and could not be in our own galaxy…..and

the idea of many different galaxies in the universe was born!

17. Edwin Hubble

A. Determined that Andromeda Galaxy outside our solar system

B. Leader in Galaxy Discovery

17. Edwin Hubble

C. Proved Hubble’s Law –The farther away a galaxy is, the faster it is

moving away.

D. All galaxies are expanding away from each other.

Hubble proved this by plotting galaxy speed and distance, and using H: the Hubble Constant ≈70. We built the Hubble Telescope to help us narrow down

this number.

Radio Galaxies- very bright, elliptical, emit radio waves.

Quasars- star-like objects that have unique spectra, at the center of a galaxy. They have large redshifts, proving they are VERY far away.

Could these objects be black holes??

It takes light a long time to travel through the universe. So when we see the light from

different objects, we are really seeing it as it was back in time. Example: It takes light 8

minutes to go from the Sun to us….so we see the Sun as it was 8 minutes earlier!

18. Cosmology

A. Cosmology is the study of the universe, how it began, what it’s like now, and how it will evolve.

B. We think the universe is about 13.5 billion years old.

C. Big Bang Theory - the universe began as apoint and is expanding outward. Most people agree with this theory.

Cosmic background radiation is very weak radiation, like “background noise” that exists everywhere in the universe. We believe this

radiation is leftover from the hot radiation from the Big Bang. This is further evidence for the

Big Bang Theory.

The universe has 3 future scenarios:

1.) It is open and will expand forever.

2.) It is closed and will one day contract.

3.) It is flat and will eventually stop expanding, but not contract.

Right now, all data appears to show that the universe is open and will expand forever. In fact, right now we have proved that the universe is expanding faster than it used to be. We can study the rate of expansion to determine what will happen.