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Prologue

Prologue. Seasons/Theories. Outline. Outside Lab Notes RA/Dec 0.2 Earth’s Orbital Motion. Day to day changes Seasonal changes Long term changes Scientific Theories SETI at home. Homework Due Wednesday. Lab Notes. Resources Part 2 in class this week. Noontime Sun for Friday

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Prologue

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  1. 1

  2. Prologue Seasons/Theories 2

  3. Outline • Outside Lab Notes • RA/Dec • 0.2 Earth’s Orbital Motion. • Day to day changes • Seasonal changes • Long term changes • Scientific Theories • SETI at home. • Homework Due Wednesday 3

  4. Lab Notes • Resources Part 2 in class this week. • Noontime Sun for Friday • Box outside Berndt 671. • Sunset, Part1 for next Monday • Note link to http://www.printfreegraphpaper.com/ • Box outside Berndt 671. • Binocular Lab Thursday, Monday(?). • Sign up… 4

  5. Homework Notes • In Mastering Astronomy - make sure your ID is the same as your FLC ID. 5

  6. Your Folder • Cut open “closed” folders. • Full name on the tab • BIG name on the front • Major on upper right • Class on lower left • A comment about yourself on the lower right • Inside - your most recent, or current, math class (subject, course number, and year taken.) • Include your daily three minute papers! You can reuse pages, just add the date. 6

  7. Three Minute Papers • Remove all spiral notebook fringe! • Re-use pages - save trees • Include date • Say something SPECIFIC. Don’t say “I learned ABOUT…” unless you say what about it you learned. Instead, say “I learned THAT…” • Bad: I learned about the velocity equation • Good: I learned that v = x/t 7

  8. Introduction The Celestial Sphere 8

  9. Oslo, Norway is 60°N latitude. How high does the star Polaris appear? A) 0° B) 30° N C) 60° N D) 90° N 9

  10. What is the southernmost declination line visible from Oslo (at 60° N)? A) 60° N B) 30° N C) 0° D) 30° S 10

  11. What is the southernmost declination line visible from Oslo (at 60° N)? A) 60° N B) 30° N C) 0° D) 30° S 11

  12. Scale on Meridian • Declination at zenith (overhead) is your latitude • The celestial equator (0° dec) is to the south of your zenith by latitude amount. • The celestial pole (90° dec) is your latitude amount above the north horizon. • http://wps.aw.com/aw_chaisson_bg_6_mx/120/30970/7928552.cw/index.html 12

  13. Right Ascension • Right Ascension corresponds to longitude. • Units are Hours (and minutes and seconds). • The trick (as with longitude) is to decide on the zero point. • Longitude zero is at the observatory in Greenwich England. • RA zero is where the sun crosses the celestial equator going north. • RA is always moving w.r.t. longitude. 13

  14. Figure P.3The Northern Sky 14

  15. How long is the exposure? Enter the correct number of hours. A) 4 B) 5 C) 6 D) 7 E) 8 15

  16. Earth’s Orbital Motion • Day to day changes • Seasonal changes • Long term changes 16

  17. 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. 17

  18. Figure P.5Solar and Sidereal Days 18

  19. Solar vs. Sidereal day • Edmund Scientific Star and Planet Finder • The view of the night sky changes during the year. 19

  20. Figure P.6The Zodiac 20

  21. Seasonal changes • One sentence - why we have seasons. 21

  22. 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. 22

  23. 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. 23

  24. 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. 24

  25. 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. 25

  26. Seasonal changes 26

  27. 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. 27

  28. Figure P.8Seasons 28

  29. 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. 29

  30. 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) 30

  31. Figure P.7Ecliptic 31

  32. Scale on Meridian • Declination at zenith (overhead) is your latitude • The celestial equator (0° dec) is to the south of your zenith by latitude amount. • The celestial pole (90° dec) is your latitude amount above the north horizon. • http://wps.aw.com/aw_chaisson_bg_6_mx/120/30970/7928552.cw/index.html • Lab note - at the equinoxes, the sun is ON the celestial equator. At the solstices, the sun is north (or south) of the equator by 23.5° (the Earth’s tilt). 32

  33. Long Term Changes • The Earth’s tilt wobbles • Precession takes ~26,000 years. 33

  34. Figure P.9Precession 34

  35. Introduction Scientific Theory 35

  36. 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.” 36

  37. 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. 37

  38. Discovery 1-1aThe Scientific Method 38

  39. 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 39

  40. SETI@home 40

  41. Chapter 18Is There Intelligent Life Elsewhere in the Universe? 41

  42. Are we alone in the Milky Way? A) definitely B) probably C) maybe D) probably not E) no way 42

  43. 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 43

  44. Figure 18.7Drake Equation 44

  45. 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?) 45

  46. The Drake Equation • Make your own estimate for the unknown values and calculate and answer for the Drake equation. 46

  47. 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. 47

  48. 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! 48

  49. 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. 49

  50. Scale of the Universe 50

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