1. The Sun, moon, and earth as a system
Section 22C

2. The sun’s motions Apparent motion Actual motion
The sun’s motion across the sky as we see it
Caused by the earth’s rotation
Ecliptic – the line marking the apparent path of the sun against the background of the stars as the sun moves around the earth.
Actual motion
Rotates on it’s axis every days
Orbits the center of the Milky Way galaxy
300 km/second
Moving toward the constellation Hercules
The sun is moving toward a point on the eastern side of the constellation Hercules.

3. The Earth’s motion Revolution Rotation Around the sun once a year
Elliptical orbit
Elliptical plane
Counterclockwise around the sun
Rotation
On its axis (tilted 23½ degrees)
Every 24 hours
Counterclockwise as viewed from the north pole
The sun and earth are the only two bodies in the solar system that lie exactly on the elliptical plane.
Revolution and orbit can be used interchangeably.
The earth revolves counterclockwise to the sun as viewed from above the elliptical plane.
The earth rotates from east to west as from above.

4. The Moon’s Motions Revolution Rotation Elliptical orbit
Around the earth
On its axis (tilted 5.4 degrees)
Counterclockwise as viewed from above
Average distance from the earth is 384,400 km
Perigee – 362,600 km
Apogee – 405,400 km
Rotation
The moon’s orbital period is equal to its rotational period.
Libration – the slight wobbling of the moon as it orbits
All of the objects in our solar system have an elliptical orbit.
Average distance – 238,900 mi
Perigee – 225,400 mi
Apogee – 252,000 mi
Moon looks slightly larger at its perigee.
Sometimes we can see “beyond the edge” of the moon’s face at times because of its libration.

5. The moon’s phases

6. terms
Lunar phase – the shape and change of the lighted face of the moon
Near side – always faces Earth
Far side – always faces away from Earth
Light side – surface of the moon facing the sun
Dark side – surface of the moon in shadow
Terminator – line between dark and light sides
Waxing – gradually increasing
Waning – gradually decreasing

7. Bell Ringers
Learning Target: I can describe a solar and a lunar eclipse.
Bell Ringer: Draw and label the phases of the lunar cycle.
Selenology – study of the moon’s geology

8. Times and seasons
Two reference points for marking days, months, and years
sidereal – distant star (coming back to the same place on ecliptic plane)
solar or synodic – sun

10. Sidereal month – 27.3 days
Synodic month – days

11. The year Julian year – 365.25 days Calendar year – 365 days
Leap year – includes one extra day
Every four years

12. The month
Time it takes the moon to make one complete orbit of the earth
Synodic month – days
Lunar month

13. The day One full rotation of the earth
The time from one local noon to the next

14. The seasons
Repeated, natural changes in temperature, precipitation, and the amount of daylight
Caused by the revolution and tilt of the earth

15. The Seasons
Summer solstice – north pole is pointed directly at the sun
The sun’s rays hit the Tropic of Cancer at 90 degrees
Longest day of the year
June 21
Winter solstice – south pole is pointed directly at the sun
The sun’s rays hit the Tropic of Capricorn at 90 degrees
Shortest day of the year
December 21

16. The seasons
Equinox – the poles are not pointing toward or away from the sun
Equal light and dark hours
Spring equinox – March 20
Fall equinox – September 20

17. eclipse
One astronomical body blocks the sun’s light to another body

19. Solar eclipse The moon blocks the sun’s light
The moon must be in one of the two points in its orbit where it crosses the ecliptic plane.
The moon must come between the sun and the earth.
Total solar eclipse – the moon completely blocks the sun
Umbra – area of total darkness
Only lasts a few minutes
Partial solar eclipse – only part of the sun is blocked
Penumbra – partial darkness
Umbra is only about 100 miles wide

21. Image provided by: Maximilian Reuter; Maximilian's website
Summary Author: Maximilian Reuter; Susanne Pfeifer; Jim Foster
August 2011 Earth Science Picture of the Day Viewer's Choice
The image above shows the total solar eclipse of March 29, 2006 as observed from the MSG satellite, in geostationary orbit 22,369 mi (36,000 km) above the equator. Note that the eclipsed area, where the shadow of the full Moon reached the Earth's surface, lies over the cloudless, east central Sahara Desert. The region that experienced a total solar eclipse at the time this image was acquired (10:00 UTC) is located at the center of the deeply shadowed region (umbra). This region has a diameter of about 112 mi (180 km). The dark region (penumbra) just outside the deepest shadow experienced a partial solar eclipse.

22. Annular eclipse – moon is at its apogee and doesn’t completely block the sun

23. Lunar eclipse The earth blocks the sun’s light from the moon
Only happens at a full moon
Moon’s orbit must be at the ecliptic

25. Tidal Forces
The gravitational pull of the sun and moon can create ocean and earth tides
Earth tides – the earth’s crust is pulled – up to 55cm
can affect earthquake and volcanic activity