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Download motions of the earth - Sonoma Valley High School
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22.2 The Earth-Moon-Sun System MOTIONS OF THE EARTH The motions of Earth are: •Rotation – turning, or spinning, of a body on its axis •Revolution – motion of a body along its orbit around some point in space •Precession – slight movement of Earth’s axis. Rotation •Results are Day and Night how long does it take for Earth to make one full rotation? Revolution •The Earth moves in an Elliptical orbit •Perihelion - Earth closest to sun 147x10 km (~January 2) 6 •Aphelion – Earth furthest from sun 152x10 km (~July 2) 6 Precession •Precession – the motion of Earth’s axis as it traces out a circle •Period for the axis to complete one full circle is 26,000 years •Earth’s axis tilt varies between 21.5° and 24.5° •Presently axis is pointing at North Star and is 23.5° Solar system in motion •Solar System speeds in the direction of the star Vega at •Solar System revolves around the Milky Way • Galaxy at speeds will take 230 million years to revolve around Milky Way Galaxy •Milky Way Galaxy is approaching the Andromeda Galaxy MOTIONS OF THE EARTH-MOON SYSTEM •Moon orbits Earth in about one month, counterclockwise • Moon’s distance to Earth varies, average of 384,401 km Why does the distance from Earth to the Moon vary? •Perigee – Moon is closest to Earth •Apogee – Moon is furthest from Earth Phases of the Moon •Phases of the moon - changes in how much of the sunlit side of the moon faces Earth •Half of the moon is lit at all times •We see a portion of the moon depending where the moon is in relation to the sun and Earth Lunar Motions •Rotates on it’s axis every 27 1/3 days •Revolves around Earth every 27 1/3 days •Same side faces Earth because period of rotation and revolution is the same ECLIPSES •Solar Eclipse – Moon moves between Earth and Sun, during new-moon phases •Lunar Eclipse – Moon moves into Earth’s shadow, during full-moon phases • An eclipse can only take places if the sun, Earth and moon are perfectly aligned During the year, how often can an eclipse happen? Why? Summary review use the following questions to write your summary 1. What are the two main motions of the Earth? 2. What is a precession? 3. Why does the same side of the moon always face Earth? 4. What kind of eclipse happens when the Earth comes between the sun and the moon?
