Class Information for PHYS/ASTR 1050 can be found at: www.physics.utah.edu Click on courses Click on The Solar Syste

1. Class Information for PHYS/ASTR 1050 can be found at: • www.physics.utah.edu • Click on courses • Click on The Solar System (George Cassiday…that’s me) • Everything about the class HW, Exams, Syllabus, etccan be found by following the appropriate links.

2. The Solar System Knowing the Heavens

3. Astronomy in ancient civilizations around the world That regions of the sky are divided around groups of stars called constellations How the sky changes from night to night How astronomers locate objects in the sky What causes the seasons The effect of changes in the direction of Earth’s axis of rotation The role of astronomy in measuring time What we cover next

4. The Night Sky Jan 27 1-hr after sunset, Colorado Springs

5. Ursa Major — The Big Dipper

6. The Summer Triangle

7. The Winter Triangle

8. The Orion Constellation

9. Why? • Is the Earth rotating CCW about an axis? • or is the sky rotating CW around Polaris?

10. Question Which of the following heavenly objects remains fixed in the sky relative to an observer's horizon? Polaris, the north star. the Moon. the Sun. Mars. the Primum Mobile.

11. The Celestial Sphere — A crystalline sphere in which all the stars are embedded surrounds the Earth and rotates CW once every ~24 hr!

12. An Early Model 8 Nested Crystalline Spheres — one each for the Moon, Sun, all of the planets (up to Saturn) and the stars.

13. Aristotle’s Cosmos — The Eight Heavenly Spheres The third book of the “Divine Comedy”, called the 'Paradiso', concerns Dante’s spiritual ascent through the heavenly spheres. The first book … the ‘Inferno‘ … concerns Dante’s descent into hell.

14. Botticelli’s Map of Hell What awaits in the 9th circle … if you don’t do your homework! The 9th Circle…

15. Latitude & Longitude • Earth’s surface is 2-d • Require only 2 numbers to specify a location. Those 2 numbers are angles.

16. Latitude & Longitude Coordinates of Peoria, Illinois 400 N 900 W 400 N 900 W

17. Celestial Coordinates

18. At North Pole, All Stars Above Horizon Never Set

19. Stars Rise & Set at Middle Latitudes

20. On Equator, Stars Rise & Set ┴ to Horizon

21. Effect Depends on Latitude

22. Day & Night • Why? • Is the Earth rotating CCW? • or is the Sun rotating CW?

23. Diurnal Motion of Stars

24. 4 Hours Later … The Earth has rotated CCW about its axis. … or has the Sun rotated CW about the Earth!

25. The Night Sky changes slowly throughout the year. • Because the Earth moves around the Sun once/year … • or the Sun moves slowly ‘backwards’ on the Celestial sphere around the Earth

26. Constellations of the Zodiac Note: ‘apparent’ position of Sun in the zodiac … could get same effect with Earth at center and Sun moving around it!

27. Constellations of the Zodiac Motion of Sun through the constellations of the zodiac

28. Solar Energy in Summer & Winter

29. Solar Energy in Summer & Winter

30. Winter & Summer The Sun is ‘in’ Cancer on Jun 21 The Sun is ‘in’ Capricorn on Dec 21 An observer on Tropic of Cancer would see Sun directly overhead at noon. An observer on Tropic of Capricorn would see Sun directly overhead at noon.

31. Winter Solstice Summer Solstice • What happens above the arctic circle? • …below the antarctic circle?

32. The Sun at 690 N. July 19

33. Suppose you stood fixed in the center not rotating. What would you see? Imagine 2 kids walking slowly CCW on a rotating Merry-go-roundund The Merry-go-round rotates fast (once/day) Kid #1 walks in a complete circle (relative to the Merry-go-round) once/year (and kid#2 once/2 years)

34. The sphere containing the stars rotates CW about Earth once/day. The sphere containing the Moon ‘slips backwards’ CCW relative to stars once/month. The sphere containing the Sun ‘slips backwards’ CCW relative to stars about Earth once/year.

35. Where is the Sun on the Celestial Sphere? Summer Solstice Autumnal Equinox Vernal Equinox Winter Solstice

36. In the winter, Sun rises in SE and sets in SW. It never rises higher than 250 above horizon (SLC). In Spring and Fall, Sun rises in E and sets in W. It rises about 48 ½ 0 above horizon (SLC). In the Summer, Sun rises in NE and sets in NW. It rises about 720 above horizon (SLC).

37. A ‘Geocentric’ Model 23 ½ 0

38. A ‘Heliocentric’ Model

39. A ‘Heliocentric’ Model

40. A ‘Heliocentric’ Model

41. Question Which hypothesis below ‘explains’ why Earth experiences 4 seasons? There are 2: (1) The fast rotating Earth slowly orbits the Sun in a plane that is tipped by 23.5o to its equatorial plane (2) The Sun moves slowly CCW along a plane that is tipped by 23.5o to the equator of the fast rotating celestial sphere. The Sun and the Earth lie in the same plane. The Earth is further away from the Sun in the winter and closer in the summer. The Sun is brighter in the summer than it is in the winter.

42. Precession of a Top

43. Precession of Earth’s Axis

44. Projection of Earth’s Axis Onto Celestial Sphere

45. Precession of the Equinoxes The Vernal Equinox moves slowly through the zodiac in step with the precession of Earth’s axis

46. Measuring Time • Solar day: • Time between 2 ‘transits’ of the local meridian by the Sun. • Sidereal day: • Time between 2 ‘transits’ of the local meridian by the Vernal Equinox.

47. Time Zones ~ 150 Intervals in Longitude

48. Sidereal Time

49. Sidereal Time 10 more (3610) for a solar day ~ 24 hr. Time to rotate 10 more is ~ 4 min. Sidereal Day is time to rotate 3610 or 23 hr 56 min.

50. Question A point on the celestial sphere that is currently in the direction of the vernal equinox will transit the local meridian … Every day at noon. Only for observers somewhere on the equator. When the Sun lies in the direction of the constellation Aquarius. Approximately 4 minutes earlier than it did on each immediately preceding solar day.