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

Do Now What are the two main motions of Earth?

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

Key Word Celestial

Vocab Words Precession Rotation Revolution

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.

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.

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)

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

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.

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?