1. Our Place in the Universe
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2. Some definitions...
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3. Star
A large, glowing ball of gas that generates heat and light through
nuclear fusion
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5. Planet
Mars
Neptune
A moderately large object that orbits a star; it shines by reflected light. Planets may be rocky, icy, or gaseous in composition.
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6. Moon (or satellite) An object that orbits a planet.
Ganymede (orbits Jupiter)
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8. Asteroid A relatively small and rocky object that orbits a star. Ida
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9. Comet A relatively small and icy object that orbits a star.
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10. Comet Lovejoy
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11. Solar (Star) System
A star and all the material that orbits it, including its planets and moons
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13. Nebula An interstellar cloud of gas and/or dust
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14. © 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley
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15. Galaxy
A great island of stars in space, all held together by gravity and
orbiting a common center
M31,The Great Galaxy
in Andromeda
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16. © 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley
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17. Universe
The sum total of all matter and energy; that is, everything within
and between all galaxies
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18. © 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley
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19. © 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley
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20. What is our place in the universe?
Our “Cosmic Address”
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21. The Milky Way Galaxy

23. Galaxies are not a ball, more like a Frisbee having little height and lots of “across.”

24. When you see the bright strip in the night sky, you are looking into the plain of the Milky Way Galaxy

26. HOW DID OUR EARTH COME TO BE?
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27. How can we know what the universe was like in the past?•
Light travels at a finite speed (300,000 km/s).
Destination
Light travel time
Moon
1 second
Sun
8 minutes
Sirius
8 years
Andromeda Galaxy
2.5 million years
Thus, we see objects as they were in the past:
The farther away we look in distance, the further back we look in time.
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28. The Milky Way Galaxy is…
About 100,000 light years across
About
1,000
Light years
tall

29. Definition: Light-Year
The distance light can travel in one year.
About 10 trillion kilometers (6 trillion miles).
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30. TEhXisApMhPoLtoE:shows the Andromeda Galaxy as it looked about
2 1/2 million years ago.
Question: When will we be able to see what it looks like now?
M31,The Great Galaxy
in Andromeda
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31. At great distances, we see objects as they were when the universe was much younger.
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32. Can we see the entire universe?
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33. Because no galaxies exist at such a great distance.
Why can’t we see auggalaxy 15 billion nlight-years away? (Assume the universe is 14 billion years old.) •
Because no galaxies exist at such a great distance.
Galaxies may exist at that distance, but their light would be too faint for our telescopes to see.
Because looking 15 billion light-years away means looking to a time before the universe existed. • •
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34. Because no galaxies exist at such a great distance.
Why can’t we see auggahlatxyQ15 billionnlight-years away? (Assume the universe is 14 billion years old.)
Because no galaxies exist at such a great distance.
Galaxies may exist at that distance, but their light would be too faint for our telescopes to see.
Because looking 15 billion light-years away means looking to a time before the universe existed. • •
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35. Wednesday, February 1, 12

36. 1.2 THE SCALE OF THE UNIVERSE
Our goals for learning:
How big is Earth compared to our solar system? • •
How far away are the stars? •
How big is the Milky Way Galaxy? •
How big is the universe? •
How do our lifetimes compare to the age of the universe?
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37. HOW BIG IS EARTH COMPARED TO OUR SOLAR SYSTEM?
(LET’S REDUCE THE SIZE OF THE SOLAR SYSTEM BY A FACTOR OF 10 BILLION;THE SUN IS NOW THE
SIZE OF A LARGE GRAPEFRUIT (14 CM DIAMETER).
an atom
a tip of a ball point pen
a marble
a golf ball
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38. SIZE OF A LARGE GRAPEFRUIT (14 CM DIAMETER).
LET’S REDUCE THE SIZE OF THE SOLAR SYSTEM BY A FACTOR OF 10 BILLION;THE SUN IS NOW THE
SIZE OF A LARGE GRAPEFRUIT (14 CM DIAMETER).
HOW BIG IS EARTH ON THIS SCALE?
A. an atom
B. a tip of a ball point pen
a marble
a golf ball
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39. THE SCALE OF THE SOLAR SYSTEM•
On a 1-to-10 billion scale:
Sun is the size of a large grapefruit (14 cm)
Earth is the size of a tip of a ball point pen, 15 meters away.
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40. HOW FAR AWAY ARE THE STARS?
ON OUR 1-TO-10 BILLION SCALE, IT’S JUST A FEW MINUTES WALK TO PLUTO.
HOW FAR WOULD YOU HAVE TO WALK TO REACH ALPHA CENTAURI?
1 mile
10 miles C. D.
100 miles
the distance across the United States (2500 miles)
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41. ANSWER: D,THE DISTANCE ACROSS THE UNITED STATES
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42. How big is the Milky Way Galaxy?
The Milky Way has about 100 billion stars.
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43. Suppose you triTedhtooucgohutntQthueemsotiroe nthan 100 billion
stars in our galaxy, at a rate of one per second…
How long would it take you?
A few weeks
A few months
A few years
A few thousand years
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44. Suppose you triTedhtooucgohutntQthueemsotiroe nthan 100 billion
stars in our galaxy, at a rate of one per second…
How long would it take you?
A few weeks
A few months
A few years
D. A few thousand years (Over 3,000!)
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45. The MilkHy oWwaybisigoinsethoef aUbnoiuvte1rs0e0?billion
galaxies.
1011 stars/galaxy  galaxies = 1022 •
stars
It has as many stars as grains of (dry) sand on all Earth’s beaches.
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46. Wednesday, February 1, 12

47. 1.3 SPACESHIP EARTH How is Earth moving in our solar system?
How is our solar system moving in the Milky Way Galaxy?
How do galaxies move within the universe?
Are we ever sitting still?
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48. How is Earth moving in our solar system?
Contrary to our perception, we are not “sitting still.”
We are moving with the Earth in several ways, and at surprisingly fast speeds.
Earth rotates around its axis once every day.
Rotates about 1000 miles/hr.
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49. E•VaEtRaYn YavEeArRag…e distance of 1 AU ≈ 150 million km.
EARTH ORBITS THE SUN (REVOLVES) ONCE
E•VaEtRaYn YavEeArRag…e distance of 1 AU ≈ 150 million km.
with Earth’s axis tilted by 23.5º (pointing to Polaris).
and rotates in the same direction it orbits,
counter-
clockwise as viewed from above the North Pole.
at a speed of 100,000 km/hr.
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50. HOW DO GALAXIES MOVE WITHIN THE UNIVERSE?
Galaxies are carried along with the expansion of the universe. But how did Hubble figure out that the universe is expanding?
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51. HUBBLE DISCOVERED THAT…
all galaxies outside our Local Group are moving away from us.
the more distant the galaxy, the faster it is racing away.
Conclusion: We live in an expanding universe.
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52. ARE WE EVER SITTING STILL?
Earth rotates on axis: > 1,000 km/hr
Earth orbits Sun: > 100,000 km/hr
Solar system moves among stars: ~ 70,000 km/hr
Milky Way rotates: ~ 800,000 km/ hr
Milky Way moves in Local Group
Universe expands
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53. © 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley
Wednesday, February 1, 12