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Prologue

Prologue. Seasons. Outline. Logistics Review HW Seasons Parallax. Logistics. Note Conversion practice page Get your folders here if you don ’ t have one yet. Scale of the Universe. Powers of Ten. http://www.wordwizz.com/pwrsof10.htm http://antwrp.gsfc.nasa.gov/apod/astropix.html.

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Prologue

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  1. 1

  2. Prologue Seasons 2

  3. Outline • Logistics • Review • HW • Seasons • Parallax 3

  4. Logistics • Note Conversion practice page • Get your folders here if you don’t have one yet. 4

  5. Scale of the Universe 5

  6. Powers of Ten • http://www.wordwizz.com/pwrsof10.htm • http://antwrp.gsfc.nasa.gov/apod/astropix.html 6

  7. Introduction Scientific Theory 7

  8. Scientific Theory • Theory - the framework of ideas and assumptions used to explain some set of observations and make predictions about the real world. • Can prove them wrong by a single bad prediction. • Can’t ever prove them “right.” They just get more widely accepted. • Eventually, some theories might be called “law,” (e.g. gravity) but they are still just scientific “theories.” 8

  9. Scientific Theory • Must be testable. • Must continuously be tested. • They should be simple. • Occam’s Razor - if two competing theories both explain the facts, then the simpler one is better. • KISS engineering - “Keep It Simple, Stupid.” • They should be elegant. 9

  10. Discovery 1-1aThe Scientific Method 10

  11. Is it possible to prove or disprove a scientific theory? A) Yes prove, yes disprove B) Yes prove, no disprove C) No prove, yes disprove D) No prove, no disprove 11

  12. Which statement about scientific theories is true? A) More complicated theories are usually better B) A theory is proven true if it makes correct predictions C) A theory must be continually tested D) Both B and C 12

  13. SETI@home 13

  14. Chapter 18Is There Intelligent Life Elsewhere in the Universe? 14

  15. Are we alone in the Milky Way? A) definitely B) probably C) maybe D) probably not E) no way 15

  16. The Drake Equation • In science, the complete lack of any useful data does not always stop us.  Instead, we proceed anyway, with a specialized equation to characterize our ignorance! • The number of advanced civilizations in our Galaxy with whom we can communicate is: N = R fp np fl fi ft L 16

  17. Figure 18.7Drake Equation 17

  18. The Drake Equation • R is the average rate of star formation (~10 stars/year) • fp is the fraction of stars with planets (current evidence - nearly 1; that is, ~100% of stars form with planets) • np is the habitable planets per star with planets (the Chaisson textbook estimates 0.1) • fl is the fraction of those planets with life (?!?) • fi is the fraction of those life-bearing planets with at least one intelligent species (?!?) • ft is the fraction of planets with an intelligent species in which that species develops technology capable of interstellar radio communication (?!?) • L is the average lifetime of a technological civilization (our society has been capable of radio communication for only about 100 years; how much longer will we remain so?  Are we a good model for other possible civilizations?) 18

  19. The Drake Equation • Make your own estimate for the unknown values and calculate and answer for the Drake equation. 19

  20. How many technological civilizations are there in the Milky Way? (N = R fp np fl fi ft L) A) 0 B) 1-9 C) 10-99 D) 102-104 E) more than 104. 20

  21. The Drake Equation • Suppose all the f terms that aren't specified above are nearly 1 (or 100%).  (optimistic!) If we do that, then the lifetime of a civilization (in years) roughly equals the number of societies in our Galaxy.  So if a technological society lasts for 100 years say, there would be 100 of them in our Galaxy. • However, even if there are 100 other civilizations capable of radio communication in our Galaxy, and even if they're interested in talking to us, the average distance between civilized worlds is about 10,000 light years - so it would take 20,000 years to get a response to any message we send. • Even if we suppose that there are 1 million civilizations out there, they'd still be separated by about 300 light years! 21

  22. The Drake Equation • Go look for ET on your own! • Run SETI@home on your computer, see: http://faculty.fortlewis.edu/hakes_c/ • SETI@home is a scientific experiment that uses Internet-connected computers in the Search for Extraterrestrial Intelligence (SETI). You can participate by running a free program that downloads and analyzes radio telescope data. 22

  23. Earth’s Orbital Motion 23

  24. Earth’s Orbital Motion • Day to day changes • Seasonal changes • Long term changes 24

  25. Day to Day Changes • Solar Day • Time from one noon to the next • 24hrs • Sidereal Day • Time that a star passes directly overhead until it does so again. • Less than 24 hrs. 25

  26. Figure P.5Solar and Sidereal Days 26

  27. Solar vs. Sidereal day • Edmund Scientific Star and Planet Finder • The view of the night sky changes during the year. 27

  28. Figure P.6The Zodiac 28

  29. Seasonal changes • One sentence - why we have seasons. 29

  30. Seasonal changes • What about seasonal changes in temperature? • Let's propose a (wrong) theory:  “the Earth is closer to the Sun in summer” • What testable predictions can we make?  (E.g., what is life like on the equator? Durango? Alaska? the North Pole? the southern hemisphere?)  Any successful theory will make correct predictions regarding length of day and temperature, which together define the seasons. 30

  31. Theory:  “the Earth is closer to the Sun in summer” Where on Earth would it be warmer at perihelion (closest approach to the Sun)? A) Northern Hemisphere B) Southern hemisphere C) Everywhere at the same time. 31

  32. Seasonal changes • Where on Earth would it be warmer at perihelion (in January)?  The answer is everywhere, unlike the reality of our world's seasons which vary by hemisphere. 32

  33. Seasonal changes • Where on Earth would it be warmer at perihelion (in January)?  The answer is everywhere, unlike the reality of our world's seasons which vary by hemisphere. • This is a huge piece of knowledge, which most Americans get wrong!  I absolutely insist that you all do better. 33

  34. Seasonal changes 34

  35. Seasonal changes • Let's look at a different view.  The left frame shows our initial theory, with no tilt.  The right frame adds a tilt to the Earth's rotation axis. 35

  36. Figure P.8Seasons 36

  37. Seasonal changes • When the sun is high, the light rays are more concentrated - the sun feels hotter. • When “your” hemisphere is pointed towards the sun, it receives more daylight hours compared to nighttime hours. 37

  38. Seasonal changes • From the point of view of the Earth, the path of the Sun in the sky appears tilted compared to Earth’s equator. • Ecliptic - The apparent path of the sun on the celestial sphere during the year. • Equinoxes - Two points where the ecliptic crosses the celestial equator. • Vernal equinox (first day of Spring ~Mar. 21) • Autumnal equinox (first day of fall ~Sept 21) 38

  39. Figure P.7Ecliptic 39

  40. Long Term Changes • The Earth’s tilt wobbles • Precession takes ~26,000 years. 40

  41. Figure P.9Precession 41

  42. The angle that the North Star (Polaris) makes with the horizon (its’ height above the horizon) changes noticeably A) as hours go by during the night B) as months go by during the year C) as you change latitude on Earth D) as you change longitude on Earth 42

  43. The angle that the North Star (Polaris) makes with the horizon (its’ height above the horizon) changes noticeably A) as hours go by during the night B) as months go by during the year C) as you change latitude on Earth D) as you change longitude on Earth 43

  44. Northern spring (March 21 to June 21) and autumn (Sept 21 to Dec 21) are the hottest seasons of the year at A) Nowhere. B) The tropic of cancer. C) The tropic of capricorn. D) The equator. 44

  45. Northern spring (March 21 to June 21) and autumn (Sept 21 to Dec 21) are the hottest seasons of the year at A) Nowhere. B) The tropic of cancer. C) The tropic of capricorn. D) The equator. 45

  46. Where along the horizon does the Sun rise on June 21 in Durango, Colorado? A) North of east B) Due east C) South of east D) Can’t tell with information given 46

  47. Where along the horizon does the Sun rise on June 21 in Durango, Colorado? A) North of east B) Due east C) South of east D) Can’t tell with information given 47

  48. Where along the horizon does the Sun rise on June 21 in Sydney, Australia? A) North of east B) Due east C) South of east D) Can’t tell with information given 48

  49. Where along the horizon does the Sun rise on June 21 in Sydney, Australia? A) North of east B) Due east C) South of east D) Can’t tell with information given 49

  50. You carefully measure the height of Polaris from Durango and from Grand Junction to the north. A) Polaris appears higher in Durango B) Polaris appears higher in Grand Junction C) Polaris is the same height in both places D) not enough information 50

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