Unit 3: Motion in the Universe
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Transcript of Unit 3: Motion in the Universe
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Unit 3: Motion in the Universe
Topic 1:Apparent Motions of Celestial Objects
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Is the Earth Moving?Evidence that Earth stands still Evidence that Earth is moving
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Apparent Motion• Apparent motion is the way an object APPEARS
to move.– Can be real, or a trick of perspective
Most celestial objects appear to move across our sky at a rate of
15o per hour
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Apparent Motion of the Stars• Some stars rise in the east, and set in the west
• Polaris remains directly above the North Pole and does not rise or set.– Some stars circle Polaris– Some stars move across the
southern sky in a shallow arc.
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Apparent Motion of the Stars
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Apparent Motions of the Planets• Planets generally follow the same east-to-west motion as
the stars, but change position over longer periods of time.
• Retrograde Motion
• Complicated motions are due to the Earth and other planets revolving around the Sun in different orbits at different speeds.
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Apparent Motions of Earth’s Moon
• The Moon has daily East to West motion, rising 50 min. later each day and shifting eastward
• One revolution around Earth = 27.3 days.
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Apparent Motions of the Sun• The Sun has a daily east to west motion– has changes in position and length of arc with the
SEASONS. – is only directly overhead between 23.5o N and 23.5o S.
latitudes
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Apparent Motions of the Sun
Polaris 42oN
WEST
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Geocentric Theory• “Earth-centered” Theory
• Earth does not rotate or revolve
• Largely accepted until the 16th Century
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Heliocentric Theory• “Sun-centered” Theory
• Earth rotates on an imaginary axis and revolves around the Sun.
• Accounts for all observations of apparent motion simply and without exceptions.
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