1. 22.2 – The Earth-Moon-Sun System – Part I

2. Do Now
What are the two main motions of Earth?

3. Do Now
What are the two main motions of Earth?
Rotation
Revolution

4. Key Word
Celestial

5. Vocab Words
Precession
Rotation
Revolution

6. Motions of the Earth Two main movements Rotation Revolution Precession
The spinning of Earth on its own axis.
24 hours
Revolution
Motion of a body, such as a planet or moon, along a path around some point in space.
Earth revolves around the Sun
365 days
Moon revolves around the Earth
Precession
Slow, slight movement over a period of 26,000 years of Earth’s axis.

8. Rotation Results of rotation are day and night.
24 hours in a day = one rotation
We can measure Earth’s rotation in 2 ways, making 2 kids of days.
Solar Day (we use this)
Time interval from one noon to the next (noon is when the sun is at the highest point in the sky) and averages 24 hours
Sidereal Day (astronomers use this)
Time interval from using a star other than our sun for one rotation and is 23 hours 56 minutes and 4 seconds.

11. Revolution Earth travels in an elliptical orbit
Travels at an average of 66, 487 miles per hour at being 93.2 million miles from the sun.
With this path there are times where Earth is closer to the sun than other time.
Perihelion
Closest to the sun (January 3rd)
Aphelion
Furthest from the sun (July 4th)

12. Earth’s Axis and Seasons
Earth's tilt is 23.5 degrees and due to this tilt Earth has its yearly cycle of seasons.
Spring Equinox
March 20 or 21
Autumn Equinox
September 22 or 23
Summer Solstice
June 21 or 22
Winter Solstice
December 21 or 22

14. Earth-Sun Motion
Our galaxy is also in constant motion like the solar system
We are heading towards another galaxy, the Great Galaxy in Andromeda.

15. Group Challenge Question
Does Earth move faster in its orbit near perihelion (January) or near aphelion (July)? Based on your answer, is the solar day longest in January or July? Why?