1. Stars and star names

3. 88 official constellations

5. α alpha i iota ρ rho β beta κ kappa σ sigma γ gamma λ lambda τ tau δ delta μ mu υ upsilon ε epsilon ν nu φ phi ζ zeta ξ xi χ chi η eta ο omicron ψ psi θ theta π pi ω omega Constellation Possessive Aries Arietis Taurus Tauri Gemini Geminorum Cancer Cancri Leo Leonis Virgo Virginis Libra Librae Scorpius Scorpii Sagittarius Sagittarii Capricornus Capricornii Aquarius Aquarii Pisces Piscium

6. Betelgeuse =  - Orionis = HIP 27989 = etc…. Mintaka =  - Orionis = HIP 29530 = etc…..

7. Objects move daily across the sky. Why?

8. North pole (Right hand rule) Because we live on a ball that’s spinning!

10. Because we live on a ball that’s spinning: N up E WRise in the East

11. because we live on a ball that’s spinning: up N E

12. N N E W Sets in the West

13. So, everything appears to move from east to west. (On a daily basis)

14. Two kinds of day! Solar day: The time it takes the earth to rotate once with respect to the sun. Trouble: The solar day changes with the time of the year!

15. Mean Solar day: The average of the solar day over a year. Our clocks measure mean solar time (MST): 1 hour = 1/24 th of a mean solar day 1 min = 1/60 th of an hour 1 sec = 1/60 th of a min

17. Sidereal Day: time between a star’s meridian crossings 1 sidereal day = 23 hr 56 min and 4.091 sec (MST) If the sidereal day is constant, why not use it to calibrate our watches? sidereal day also divided up into hour, minutes, sec (sidereal)

18. The Celestial Sphere

19. We can think of all these stars as fixed on a big celestial sphere C.S. fixed Earth spins towards East OR …

20. We can think of all these stars as fixed on a big celestial sphere Earth fixed C.S. spins towards West

21. What we see from our specific locale

22. The natural (local) way: Apparent S Horizon Apparent N Horizon Zenith N pole S pole Apparent horizons depend on your height, mtns etc …

23. The natural (local) way: Zenith N pole S pole ‘True’ (local) horizon

24. celestial N pole celestial S pole celestial equator celestial sphere rotates Polaris

25. celestial N pole celestial S pole celestial equator local horizon zenith Earth’s equator latitude

26. celestial N pole celestial S pole celestial equator local horizon Make Earth very small (Since everything is so far away!) zenith latitude Polaris latitude

27. local horizon

28. celestial N pole celestial S pole celestial equator local horizon celestial sphere rotates (instead of the earth) Motions of the stars relative to the fixed earth!

30. celestial N pole celestial S pole celestial equator local horizon zenith Blue area is below observer’s horizon

31. celestial N pole celestial S pole celestial equator local horizon zenith

32. celestial N pole celestial S pole celestial equator local horizon zenith

33. celestial N pole celestial S pole celestial equator local horizon zenith

34. celestial N pole celestial S pole celestial equator local horizon zenith

35. celestial N pole celestial S pole celestial equator local horizon zenith

36. celestial N pole celestial S pole celestial equator local horizon zenith

37. celestial N pole celestial S pole celestial equator local horizon Circumpolar!

39. celestial N pole celestial S pole local horizon: observer at earth’s equator Observer’s zenith No circumpolar

40. celestial N pole celestial S pole local horizon: observer at 45˚ N Observer’s zenith

41. celestial N pole celestial S pole local horizon: observer N pole zenith All circumpolar

42. Putting the sun’s position on the celestial sphere (The ecliptic) Earth’s tilted by 23 ½ °

44. Sun’s daily motion Sun’s yearly motion on celestial sphere

49. The seasons Earth’s tilted by 23 ½ ° Relative to the plane of its orbit around the sun

50. Axis always points in the same direction (celestial N pole)

53. celestial N pole (N) summer solstice ≈ June 21

54. celestial N pole Equinox: (N) Autumn (Autumnal) ≈ September 22 (N) Spring (Vernal) ≈ March 21

55. celestial N pole (N) winter solstice ≈ December 21

56. Why is winter cold and summer hot?

60. “Precession of the equinox”

61. The Earth isn’t a perfect sphere! Non-zero torque from sun and moon!

62. Spinning objects subjected to a torque precess!

64. Precession of the North celestial pole.