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Understanding Earth's Movements in Astronomy

Explore Earth's various motions in space, from rotation causing day and night to revolution forming seasons. Learn about precession, nutation, and the barycenter, and understand their effects on Earth's axis and orbital dynamics.

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Understanding Earth's Movements in Astronomy

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  1. Earth’s Motions Astronomy

  2. Earth’s Motions • Rotation = spinning • Counterclockwise • Causes night & day • Faster rotation= shorter days/nights • Revolution = orbit • Counterclockwise • Takes 1 year • Faster revolution = shorter year

  3. Rotation vs Revolution

  4. Seasons . . . • Caused by the TILT of Earth’s axis • NOT caused by the distance from sun! (Earth is closest in January!!!) • Axis tilt = 23.5° • Sunlight hitting hemispheres at different angles = different season

  5. Earth’s Shape • Recall: Earth rotates counterclockwise • Rotation causes Earth to “squish out” around the equator (middle). Incorrect Correct

  6. Precession • . . . is the change in direction axis points. • Experienced by all rotating objects • No change in angle of tilt = no effect on seasons

  7. Precession • Period of the Earth’s precession: 26,000 yrs • Over this time, the stars near the poles change . . . Polaris and Vegas alternate as the North Star!

  8. Nutation • . . . slight change in tilt of Earth’s axis (it wobbles!) • Change of plus or minus 0.5° from the average 23.5° angle. • Caused by: moon’s gravity only

  9. Nutation • Small change in the Earth’s tilt = small change in strength of seasons throughout the 18 year period

  10. Barycenter • All objects’ gravities pull on each other • Causes all objects to orbit around a point where their masses balance • Point of balance = barycenter • Always located close to the center of the larger object

  11. Barycenter • Example: The Moon orbits a point 1,710 km below the surface of the Earth, but this is not at the Earth’s center!

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