1. 27.3 – Sun-Earth-Moon System

2. Daily Motions
Earth’s rotation causes us to see daily rising and setting of the Sun, Moon, and stars
Rises in the East, sets in the West
We observe changes in their location due to the Earth rotating

3. Day Length Solar day – time from one noon to the next noon
Length of a day is approximately 4 minutes longer than it takes the Earth to make one rotation on its axis
Foucault pendulum

4. Earth orbits the sun in a slightly elliptical orbit
Annual Motions
Earth orbits the sun in a slightly elliptical orbit
Plane of Earth’s orbit is called ecliptic plane
This movement causes us to see different constellations in the sky during different times of year

5. Earth’s tilt The Earth’s axis is tilted 23.5°
Axis remains fixed in space
Cycle of seasons is due to this tilt
When Northern hemisphere points towards the sun = Summer
When Southern hemisphere points towards the sun = Summer

6. Solstices
The Sun is overheard at its farthest distance either north or south of the equator

7. Summer Solstice around June 21st
In Northern Hemisphere, number of daylight hours reaches its maximum
Sun is in the sky continuously with the region of the Arctic Circle

8. Winter Solstice Around December 21st
In Northern Hemisphere, number of daylight hours is at its minimum
Sun does not appear in the region within the Arctic Circle

9. Equinox
Equal nights
Earth’s axis is perpendicular to the Sun’s rays and at noon the Sun is directly overhead at the equator
Vernal – March 20, 2011
Autumn – Sept. 23, 2011

11. Phases of the Moon The moon does not produce its own light
reflects light of the Sun
The shape of the lighted portion of the moon, as seen from Earth, is known as its phases.

13. Phases of the Moon New Moon = moon is between Earth & Sun
So we do not see light reflected off of its surface
Waxing = lighted area is increasing due to position between Earth & Sun
Crescent = “sliver” of moon is visible
1st Quarter = ½ lit up
Gibbous = almost Full

14. Crescent and gibbous moons

15. Phases of the Moon Full Moon
Waning = decreasing amount of moon reflecting light due to position
Gibbous
3rd Quarter = oppose half lit up after full moon
Crescent
New Moon

16. First quarter v’s last quarter moons

17. Earthshine
Only during early crescent phases, “dark” part shines dimly, due to reflect light off the Earth

18. In-Class Assignment
Start “Movements of Earth” WKT

19. 27.3 Part B
OBJECTIVES
Describe the orbit of the Moon and its effects including cycles and eclipses.
Illustrate how the Moon goes through phases..

20. Synchronous Rotation
Moon rotates with a period equal to its orbit period
Spins only once each time it goes around the Earth

21. Lunar Motions
Lunar Month = complete cycle of phases from one New Moon to the next
Rotation = 29.5 days
Revolution of Moon = 27.3 days
Orbits around Earth
Moon rises and sets 50 minutes later each day

22. Tides Moon’s gravity pulls on Earth and creates bulges of ocean water
As Earth rotates, bulges remain aligned with moon

23. Solar Eclipses Moon passes directly between Sun and Earth
For more information see pg. 793
Moon passes directly between Sun and Earth
Blocks sunlight
Total eclipse only visible in small portion of Earth
Partial eclipse is seen in larger portion

24. A series of photos of a solar eclipse!

25. A total solar eclipse!

26. A partial solar eclipse!

27. This solar eclipse shows flares (storms) on the edges of the sun!

28. Annular eclipses Eclipse with ring of the Sun visible Moon in apogee
Due to the elliptical orbit of Moon causes it to be closer to Earth during parts of its orbit
Perigee – closest point of Moon’s orbit to Earth
Apogee – farthest point
Moon appears smaller

29. An annular solar eclipse!

30. This is the difference between a perigee and apogee moon!

31. Lunar Eclipses Occurs with Moon passes through Earth’s shadow
Earth is between Moon and Sun
Moon faintly visible because Earth’s atmosphere is filtering sun light
Lasts about 2 hours

32. Lunar eclipse – time elapsed pictures

33. Next eclipses

34. Time Zones
Because of sun’s apparent motion, sun appears highest over different locations at different times
World divided into 24 standard time zones
In each zone, noon is when sun is highest over the center of that zone

35. Earth rotates 15 degrees every hour
Time Zones
Earth rotates 15 degrees every hour
Each time zone is one hour earlier than the zone to its east
International Date Line – point where earth changes from one day to the next

37. Daylight Savings Time Change your clocks November 7th at 2 AM
Fall back an hour
Spring forward an hour
By changing your clocks, you gain an extra hour of daylight

38. Are calendars tied in with the moon?
Day: time it takes Earth to make a full rotation
Month: Time it takes the moon to go from through one cycle

39. Are calendars tied in with the moon?
Year: Time needed for the earth to make one orbit (revolution) around the sun ( days – makes us add a day every four years – leap year)
The days of the week were named after the Sun, moon, and the five known planets.

40. In-class Assignment
Finish “Movements of Earth” WKT