22.2

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22.2 The Earth-Moon-Sun System Part I
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Do Now

• What are the two main motions of Earth?

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Do Now

• What are the two main motions of Earth?
• Rotation
• Revolution

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Key Word

• Celestial

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Vocab Words

• Precession
• Rotation
• Revolution

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Motions of the Earth

• Two main movements
• Rotation
• 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 Earths axis.

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Rotation

• Results of rotation are day and night.
• 24 hours in a day one rotation
• We can measure Earths 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.

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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)

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Earths 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

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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.

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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?