Unit 3: Motion in the Universe

1. Unit 3: Motion in the Universe Topic 1: Apparent Motions of Celestial Objects

2. Is the Earth Moving? Evidence that Earth is moving Evidence that Earth stands still

3. 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 15oper hour

4. 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.

5. Apparent Motion of the Stars

7. 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.

8. 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.

9. 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

10. Apparent Motions of the Sun Polaris 42oN WEST

11. Geocentric Theory • “Earth-centered” Theory • Earth does not rotate or revolve • Largely accepted until the 16th Century

12. 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.