Motions of the Sky

1. Motions of the Sky 1. Seasons 2. Tides 3. Moon Orbit/Tidal Locking 5. Moon Phases 6. Lunar Eclipses 7. Solar Eclipses 8. Planet Retrograde Motion

2. The Motion of the Earth • Rotation –Spinning of the earth on its axis • 24 hours • 1 day • Revolution- movement of earth around the sun • 365 days • 1 year • Precession – wobble of earth on axis • 26,000 years

3. Seasons • Seasons ARE NOT caused by the changing distance between the Sun and Earth. • During the Northern hemisphere winter, we are actually CLOSER to the Sun.

4. Seasons ARE caused by: • The TILT of the Earth's axis. • The Earth is tilted 23.5 degrees

5. Seasons When it is summer in one hemisphere, it is winter in the other.

6. Apparent motion of the Sun • we do not perceive the Earth moving (Instead the sun appears to move.) • Ecliptic – The apparent path of the sun

8. Apparent Motion of the sun • Summer • more direct sunlight, • sun appears to be higher in the sky. • Higher on the ecliptic • Winter • less direct sunlight • sun appears to be lower in the sky. • Lower on the ecliptic

9. What Causes the seasons? • spring and fall • we get equal light as the opposite hemisphere. • (The sun in on the celestial equator). • Therefore, the seasons are determined by the suns position on the ecliptic.

10. Seasons Summer Solstice - June 21 - 22. The sun is at the highest point along the ecliptic. The first day of summer and longest day of year.

11. Seasons Summer Solstice - June 21 - 22. The sun is at the highest point along the ecliptic. The first day of summer and longest day of year. Fall (Autumnal) Equinox - Sept. 22 - 23. The sun crosses the celestial equator heading south. The first day of fall. Equal length of day and night.

12. Seasons Summer Solstice - June 21 - 22. The sun is at the highest point along the ecliptic. The first day of summer and longest day of year. Fall (Autumnal) Equinox - Sept. 22 - 23. The sun crosses the celestial equator heading south. The first day of fall. Equal length of day and night. Winter Solstice - Dec. 21 - 22. The sun reaches the lowest point on the celestial sphere. The first day of winter and the shortest day of the year.

13. Seasons Summer Solstice- June 21 - 22. The sun is at the highest point along the ecliptic. The first day of summer and longest day of year. Fall (Autumnal) Equinox- Sept. 22 - 23. The sun crosses the celestial equator heading south. The first day of fall. Equal length of day and night. Winter Solstice- Dec. 21 - 22. The sun reaches the lowest point on the celestial sphere. The first day of winter and the shortest day of the year. Spring (Vernal) Equinox- March 20 - 21. The sun crosses the celestial equator heading north. The first day of Spring. Equal length of day and night.

14. Seasons

15. Earth/Moon System Scale Diagram of Earth/Moon System

16. What causes tides?: Just as the Earth pulls the Moon, the moon also slightly pulls on the Earth.

17. Tides Basics: • Tides: • The moon pulls on everything on Earth. • since water is fluid, the Earth cannot hold onto it and the • moon is able to pull on it. • -This creates two tides per day. • (The continents are also pulled, but much less so, only about • 30 cm. This is not noticeable)

18. Tides: Tidal forces created by one large body on another

19. Sun Tides: Tides Caused by the Sun: The Sun is also pulling on the Earth, causing tides, but to a much smaller extent

21. Spring Tides • Spring Tides -When the Sun and Moon align, and the gravitational pull combine, we get extra high tides.

22. Neap Tides: Neap Tides -When the Sun and Moon are at right angles, the gravitational pull cancels, and we get extra small tides.

27. Tides: The Bay of Fundy between Nova Scotia and Main has the worlds most extreme tides. Tides can raise and lower by 48 feet. http://www.youtube.com/watch?v=_J2AtORivSY http://www.youtube.com/watch?v=SOAKZLwHhXU http://www.youtube.com/watch?v=ycNzUAp6OXk

28. Tides:

29. Tides: • Tidal forces causes • The Rotation of the Earth to slow down. • (This Causes Precession) • Length of day = 6 hrs 4.5 billion years ago (formation of Earth) • Length of day = 20 hrs 300 Million years ago (Devonian time period) • Length of day = 23 hrs 80 million years ago (Cretaceous - Dinosaurs) • 2. The moon to drifting away. • It drifts away 4 cm a year, which is slowly increasing the length of the month. • (Verified by Mirrors placed on Moon during Apollo Missions) 3. Tidal Locking.

30. Tidal Locking (Phase Locking)

31. Tidal Locking (Phase Locking) Tidal Locking: Although the moon rotates AND revolves, people on Earth only see 1 side of the moon. Tidal locking causes 1 rotation of the moon to be equal to 1 revolution of the moon (1 rotation = 1 revolution)..

32. Tidal Locking (Phase Locking)

33. Tidal Locking (Phase Locking) Tidal locking is normal. Objects that are tidally locked: Moon to Earth Phobos and Deimos to Mars Most of Jupiter and Saturn's Moons. Pluto and Charon Probably Neptune's and Uranus's moons (not enough data) Mercury to the Sun

34. The Moon • The moons orbit is not circular, it is elliptical. • This means the moons distance from earth changes over the course of a month.

35. Moon Distance Perigee vs Apogee

36. Perigee and Apogee

37. Moon Distance Perigee vs Apogee Scale diagram of Earth/Moon system

38. The Moon at Perigee and Apogee Perigee - The moons closest approach to earth. (356,000 km) Apogee - The moons farthest distance from earth. (407,000 km)

39. Moon Phases

40. Moon Phases Caused by: the angle at which we view the moon as it orbits the Earth.

41. Moon Phases • What is happening: • The sun always shines on 1/2 of the moon. • Depending on the angle at which we see the moon, • we see different parts of the moon lit up at different times.

42. Moon Phases

43. Moon Phases

44. Moon Phases

45. Lunar Eclipses

47. Cause of Eclipses

48. Cause of Eclipses

49. Lunar Eclipse – Occurs when the moon passes through the Earth’s shadow. This only occurs during a FULL moon phase, twice per year.