Earth - Sun - Moon Relationships: Annual Motions/Seasons


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Earth - Sun - Moon Relationships: Annual Motions/Seasons

  1. 1. Annual Motions: What causes the seasons? Earth Science
  2. 2. Cornell Notes Rotation 2) Revolution 3) Earth’s orbit 1)
  3. 3. Astronomy Basics…  Rotation – when a planet spins on its axis. It takes 24 hours for Earth to spin on its axis once.
  4. 4. Astronomy Basics…    Revolution – The time it takes when an object goes around a sun or planet. It takes 365 days for Earth to revolve once around the Sun. It takes 30 days for the moon to revolve around Earth.
  5. 5. Astronomy Basics…    Earth’s orbit – The Earth’s orbit is Eccentric (oval-shaped). Perihelion – closest to the sun. Aphelion – farthest from the sun.
  6. 6. Basic Concepts…(We will refer to the NORTHERN HEMISPHERE.) 1) Not caused by the Earth’s distant from the sun!!!  Aphelion – Earth is 94.5 million miles away from the sun (IN JULY).  Perihelion – Earth is 91.5 million miles away from the sun (IN JANUARY).
  7. 7. 2) Caused by the Earth’s tilt of the AXIS: 23.5°.  The Earth’s Axis remains at a fixed place (as it orbits around the sun), so that, at one point, the northern hemisphere of Earth is tilted toward the sun, while at another point six months later, the northern hemisphere is tipped away from the sun.
  8. 8. 3) Tropic of Cancer  23.5 N Latitude
  9. 9. 3) Tropic of Capricorn  23.5 S Latitude
  10. 10. How does the angle affect our seasons?  As the winter solstice approach, the amount of daylight is decreased. Why? During the winter, the sun’s rays will not hit our area directly. The sun appears to be at a lower altitude.
  11. 11.  In contrast, during the summer, the sun hits our area more directly and the sun appears to be at a higher altitude.
  12. 12. Vernal Equinox: • Spring Vernal Equinox • March 21. • hits equator directly • average angle of insolation. • equal amts of day and night Summer Solstice Winter Solstice Autumnal Equinox: • Solstice: Autumnal Equinox WinterAutumn/Fall Summer Solstice: • Sept 21. • winter • Sun hits the N. Hemisphere directly (Tropic of Cancer 23.5 N). hits • Dec• 21. equator directly • June 21 – 22. • longest amount of daylight • high angle of insolation. • average • shortest day. angle of insolation. • sun hits @ S. Hemisphere • equal amts of day of directly at 23.5 S. (Tropicand night/ Capricorn). • low angle of insolation.
  13. 13. Angle of insolation - The angle at which the sun's rays strike a particular location.
  14. 14. Only latitudes between the tropic of cancer and Tropic of Capricorn can receive direct rays. The maximum angle of insolation is 90 degrees.
  15. 15. • The angle of insolation varies with: • 1) Season - The maximum angle of insolation, maximum duration, and maximum intensity occur during the summer. • 2) Latitude - As latitude increases, the angle of insolation decreases • 3) Time of day- From morning to noon the angle of insolation increases and the from noon to evening the angle of insolation decreases. Q: When is the best time to get a tan during the summer? 12 noon or 6 pm? Why?
  16. 16. • As the angle of insolation increases, the sun gets higher in the sky. As the sun gets higher in the sky the length of the shadow decreases. Effect 1: a) Winter – Our shadows are longer at noon (angle in low). b) Summer – Our shadows are shorter at noon (angle is high).
  17. 17. Effect 2: a) Winter – The duration (amount of time) of daylight is shorter. b) Summer – The duration of daylight is longer. Effect 3: a) Winter – intensity (heat) of insolation is low. b) Summer – intensity of insolation is higher.