Download - Unit 3: Motion in the Universe
Unit 3: Motion in the Universe
Topic 1:Apparent Motions of Celestial Objects
Is the Earth Moving?Evidence that Earth stands still Evidence that Earth is moving
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
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.
Apparent Motion of the Stars
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.
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.
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
Apparent Motions of the Sun
Polaris 42oN
WEST
Geocentric Theory• “Earth-centered” Theory
• Earth does not rotate or revolve
• Largely accepted until the 16th Century
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.