Eclipses -- interesting Phenomena

• Shadows -- two degrees of intensity

  • umbra -- totally dark -- all of Sun blocked
  • penumbra -- only part of sun blocked
  • demo with flashlight and finger
  • draw angles on blackboard fig. 3-10

• Two types

  • Solar -- Moon’s shadow hits the Earth
    • If the umbra (dark) -- total
      • by far the most impressive eclipse
      • angular size of the Moon slightly larger than Sun (0.5o)
        • In the past, the Moon was closer. Recall: Tides cause the Earth’s spin to slow. To conserve angular momentum, Moon must move outward. fig.3-14
        • or -- look at forces of Earth on Moon fig.3-9
        • total eclipses more frequent and widespread in past

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