Stars vs. Planets

1. Stars vs. Planets Init 4/24/2009 by Daniel R. Barnes WARNING: This presentation includes both graphical elements created by the author and graphical elements taken without permission from the world wide web. Do not copy or distribute.

2. California Earth Science Standard 1d: Students know the evidence indicating that the planets are much closer to Earth than the stars are.

3. some distances . . . Earth = 8000 miles wide

4. some distances . . . The space shuttle orbits from an altitude of 200 miles above the earth’s surface.

5. some distances . . . 200 miles may sound high up, but compared to the 8000 mile diameter of the earth, 200 miles is nothing. Seen from this viewpoint, the space shuttle is barely off the ground!

6. some distances . . . Geosynchronous satellites, used widely for tv broadcasts and other communications applications, orbit at an average altitude of 22,300 miles.

7. The “space shuttle” was not designed to go to the moon, and it simply can’t make it there. X HOWEVER . . .

8. The “space shuttle” was not designed to go to the moon, and it simply can’t make it there. HOWEVER . . . The Apollo missions, powered by the Saturn V rocket shown here, DID make it to the moon several times in the 60’s & 70’s.

9. “lem” Lunar module Lunar rover = “moon buggy”

10. In this diagram, the earth and moon look far too large compared to the distance between them . . . A more realistic picture would have them only this big: The moon looks a little farther away that way, doesn’t it? The average distance between the earth and its moon is about 240,000 miles

11. The average distance between the earth and the sun is about 93,000,000 miles 93,000,000 miles is also known as one “astronomical unit”. 93,000,000 miles = 1 AU The sun is about 400 times as far from the earth as the moon is, but it’s 400 times wider than the moon, so they seem to be the same size to us.

12. Mars, the “red planet”, is the 4th planet from the sun. Its orbit lies between those of Earth and Jupiter Mars will probably be the first planet humans set foot on.

13. 36,000,000 miles 250,000,000 miles Mars Earth Sun The distance from Earth to Mars varies from 36 to 250 million miles, depending on where the planets are in their orbits around the sun.

14. Neptune is the 8th true planet. It’s farther from the sun than Uranus, but it weighs more. When astronomers downgraded Pluto from “planet” to “dwarf planet”, Neptune was, from then on, regarded as the farthest planet from the sun.

15. Neptune Neptune’s orbit Earth’s orbit Earth Sun Neptune is about 2,800,000,000 miles from the sun. That’s 30 times as far as Earth’s 93,000,000. Neptune is 30 AU from the sun . . . and about that far from Earth, too.

16. Light travels 186,000 miles per second. 186,000 is a big number, but it’s not infinity. Light takes time to travel. Over short distances, it’s not noticeable, but over long distances, it makes a difference. Light takes a little more than 8 minutes to travel the 93,000,000 miles from the sun to the earth. In one year, light can travel 5,878,630,000,000 miles. That distance, which is almost 6 trillion miles, is called . . . . . . a “light-year” A light-year is about 6 trillion miles . . . of DISTANCE

17. Proxima Centauri, seen here in an x-ray photo taken from the Chandra X-ray observatory in outer space, is the second-closest star to the earth. (The closest star to the earth is the sun.) Proxima Centauri is 4.2 light-years from Earth. That’s about 24,000,000,000,000 miles That’s about 15,000 AU The closest star to the earth (besides the sun) is 500 times farther away from Earth than Neptune, the farthest planet

18. The Milky Way Galaxy, in which our whole solar system is just a tiny speck, is 100,000 light years across. The stars in our own galaxy are anywhere from 4 ly to just under 100,000 ly away from us. That’s FAR.

19. The Milky Way Galaxy is just the galaxy we live in. There are more than 100,000,000,000 galaxies in the observable universe. One of the closest galaxies to the Milky Way is the Andromeda Galaxy, which is 2 million ly away.

20. Wow. Stars are far away.

21. 1d. Students know the evidence indicating that the planets are much closer to Earth than the stars are. So what's the evidence?

22. *Planets move a lot more than stars do. *When seen through a telescope, planets are round discs, not just points of light. In fact, with a telescope, you can see detailed surface features of planets, but not so with stars. *The “parallax” method of determining distance shows stars to be farther than planets. (useful only for the nearer stars) *Radar shows not only how far away planets are, but the change in frequency of the echoes tells us their motion, as well. *We have successfully flown unmanned probes past all of the planets in the solar system, but we haven’t even come close to getting a probe to a star other than the sun.

23. *Faraway stars are very dim, much dimmer than planets, especially than planets close to the earth like Venus. *Planets pass in front of stars as they move through the sky, blocking them from view. *Planets orbit our sun, but stars don’t. Planets are part of our local solar system, but stars are much farther away. Let's look at some of these items in detail.

24. A

25. Exihibit A: Planets move a lot more than stars do. The stars rise in the east and sink in the west as the night goes by, but the pattern they form is pretty constant. The most famous star patterns in the night sky have names. They are called “constellations”. This is the first one I ever learned. It’s called the “big dipper” It’s supposed to look like a big spoon or something.

26. In the city, where I live, it’s hard to see constellations well at night because of the city lights, but I can usually see the three bright stars in Orion’s belt.

27. Here, a picture of Orion, a hunter from ancient Greek mythology, is superimposed over the constellation so you can see what the ancient Greeks imagined when they looked into the sky.

28. Perhaps the most discussed constellations are the twelve signs of the zodiac. The stars in these patterns have moved a bit since the ancient Greeks named them, but the tradition continues.

29. The stars in the night sky mostly seem to remain in the same place relative to one another.

30. From one night to the next, some of them seem to change position.

31. The ancient Greeks noticed these, and called them “planets” (or whatever the exactly Greek word is), which means “wanderers”.

32. Have you noticed the wandering star in these slides?

33. The wandering “star” is actually a planet.

34. The ancient Greeks couldn’t see all of the planets back then, but they did know about Mercury, Venus, Mars, Jupiter, and Saturn. Back then, when people still thought the whole universe revolved around the earth, the sun and moon were considered to be planets, also.

35. When you drive down a highway through the countryside, the asphalt on which you drive moves so fast past you that if you look straight down at it, it is a grey blur. Fence posts along the side of the road whiz by pretty fast, too, but not as fast as the road surface beneath your tires. If there are trees beyond the fence, they go by pretty fast too, but not as fast as the fence posts. The mountains in the distance hardly seem to move at all. If the moon is in the sky, it will seem to be totally motionless. The farther away something is, the slower it SEEMS to be moving. The fact that planets look like they’re moving faster than the stars in the sky is evidence that the planets are closer to us than the stars are.

36. B

37. Exihibit B: When seen through a telescope, planets are round discs, not just points of light. In fact, with a telescope, you can see detailed surface features of planets, but not so with stars. . . . nearly as detailed and clear as this picture of Jupiter? Is this picture of the star Proxima Centauri . . .

38. C

39. Exhibit C: The “parallax” method of determining distance shows stars to be farther than planets. (useful only for the nearer stars) Earth A relatively nearby star Sun

40. Exhibit C: The “parallax” method of determining distance shows stars to be farther than planets. (useful only for the nearer stars) At one time of the year, a star may seem to be off in one direction . . .

41. Exhibit C: The “parallax” method of determining distance shows stars to be farther than planets. (useful only for the nearer stars) But six months later, when the earth is on the other side of the sun, the star will appear to be off in a different direction.

42. Exhibit C: The “parallax” method of determining distance shows stars to be farther than planets. (useful only for the nearer stars) If you know the diameter of the earth’s orbit, you can use the mathematical trick of “trigonometry” to calculate the distance to the star.

43. D

44. Exhibit D: Radar shows not only how far away planets are, but the change in frequency of the echoes tells us their motion, as well. This is the 250 foot-wide Mk1 radio telescope. I’m not sure if it sent or received the signal or both, but it was definitely involved in the following . . .

45. In 1957, the Mk1 radio telescope (or an associated device) sent a radio wave pulse to the planet Venus when it was at the point in its orbit when it was as close as it ever gets to Earth.

46. The radio wave pulse took 2 minutes to get to Venus and 2 minutes for its echo to travel back to Earth. Knowing that light travels 186,000 miles per second, astronomers were able to calculate that Venus was 41 million miles from Earth at this point in its orbit.

47. E

48. Exhibit E: We have successfully flown unmanned probes to all of the “true” planets in the solar system, but we haven’t even come close to getting a probe to a star other than the sun. Mariner 9 reached Mars in 1971. It took some pictures and sent them back using coded radio signals.

49. The Cassini-Huygens probe was launched in 1997.

50. The Cassini-Huygens probe took several months to fly past Jupiter, but it reached its closest point in 2000. It took some very detailed pictures and made lots of measurements.