1. Formation of the Solar System and The Universe

2. Our Solar System Sun is the center of a huge rotating system of:
Planets
Their satellites
Smaller bodies
Most of the mass of solar system is the sun (99.85%)

3. Our Solar System Planets move in elliptical orbit
All in same direction
Terrestrial planets = small and rocky
Mercury, Venus, Earth, Mars
Jovian planets = huge gas giants
Jupiter, Saturn, Uranus, Neptune

4. Formation of the Solar System
Between stars = gas and dust
Nebula = cloud of gas and dust
Hydrogen, helium, heavier elements
Nebula begin rotating slowly and contract because of gravity
Clouds contract --> spin faster

5. Nebular Theory
Nebular theory states that the sun and all bodies in the solar system formed from a rotating disk of interstellar gas and dust.
4.6 billion years ago
This cloud is roughly spherical and so dense that it begins to collapse under its own gravity

6. Nebular Theory
As the speed of rotation increased, the center of the disk flattened.
The dense center formed the sun and planets formed along the flattened, nebular cloud
Nebular theory

7. Planetesimals Planetesimals = small, irregularly shaped bodies
Solid bits of matter collided and clumped together = accretion
Planetesimals grew larger
Enough mass --> exert a gravitational pull on other objects
Grew into planets

8. Birth of Planets Inner solar system = close to sun
Temperatures high
Only metals and silicate minerals
Too hot for ices of water, carbon dioxide
Outer solar system = cold enough for ices of water
Accumulations of solid bits of material and large quantities of ices
Large enough to capture gases (hydrogen and helium) --> grew into giants

9. Galaxies
Galaxies = groups of stars, dust, and gases held together by gravity
Our galaxy = Milky Way
More than 100 billion stars in Milky Way
Looks milky because the solar system is located within a flat disk
We view it from inside and see stars in every direction

10. The Milky Way Galaxy Interstellar matter blocks our vision
Radio telescopes
Size = large spiral galaxy
Disk = 100,000 light-years wide
Nucleus = 10,000 light-years thick
Milky Way = taken by a camera mounted on a satellite

11. The Milky Way Galaxy Structure At least 3 spiral arms
Sun is in one of these arms about 2/3 of the way from the center
Stars in arms rotate around the nucleus
Outermost arms move slowest

12. Types of Galaxies Spiral Galaxies Elliptical Galaxies
Irregular Galaxies

13. Spiral Galaxies Disk-shaped Greater concentration of stars near center
Arms extend from nucleus
Both young and old stars
Youngest in arms
20% of all galaxies
Barred spiral = stars arranged in shape of bar
Milky Way?
10% of all galaxies

14. Elliptical Galaxies Round to oval Most are small No spiral arms
Contain old stars
60% of all galaxies

15. Irregular Galaxies Irregular shapes Made up of mostly young stars
10% of all galaxies

16. Galaxy Clusters Galaxies grouped in clusters
May contain thousands of galaxies
Our cluster contains galaxies
Galaxy clusters make up superclusters

17. The Expanding Universe
Doppler Effect = perceived change of wavelength of a wave that is emitted from a source that is moving away or toward an object
Wave appears to be “stretched” as source moves away from you
Wave appears to be “squished” as source moves toward you

18. The Doppler Effect
Light from a source moving away from you appears redder
Waves are lengthened
Moving toward you appears bluer
Waves are shortened

19. How are Doppler shifts measured?
From dark lines in spectrum
Comparing them with standard spectrum
We’ll talk about this more in depth when we discuss stars

20. Doppler Effect in Astronomy
Determines whether a body in space is moving way from or toward Earth
Large Doppler shifts = higher speeds
Small Doppler shifts = slower speeds

21. Red Shift Most galaxies have Doppler shifts toward red end of spectrum
Earth and source are moving away from each other

22. Hubble’s Law Greater red shifts = faster speeds
Hubble’s Law = more distant galaxies have greater red shifts --> they must be moving away from us at a speed that is proportional to their distance
Red shifts of distant galaxies tell us that the universe is expanding

23. The Big Bang Remember…all galaxies are moving away from us
We are not at the center of the universe
Big Bang = the universe began as a violent explosion from which the universe continues to expand, evolve, and cool
Universe was a dense, hot, supermassive ball
13.7 billion years ago --> violent explosion --> material hurled in all directions
All matter and space created
Atoms formed
Gases cooled and condensed --> formed the stars

24. Evidence for the Big Bang
Red shift of galaxies
Universe is still expanding
Cosmic background radiation = energy
Coming from every direction in space
Produced during big bang

25. How will the universe end?
Will it last forever?
Stars slowly burn out
Invisible matter, black holes, dark and cold universe
The Big Crunch?
Galaxies stop moving away
Gravity pulls back in (critical density)
Combine into high-density, high-energy mass
Fiery death