1. Celestial Objects and Motions

2. What keeps objects in orbit?
the force that attracts a body toward the center of any other physical body having mass.
Gravity -
Inertia
property of matter by which it continues in its uniform motion in a straight line
Dynamic equilibrium

3. PLANETARY MOTION Models
Geocentric Model (Aristotle) – earth centered
Geo = Earth
Did not explain retrograde motions of some planets

4. PLANETARY MOTION Models
Heliocentric (Copernicus) – Sun centered
Helio = Sun
Everything revolves around the sun

5. Motions of Celestial Objects
1. The celestial sphere describes the dome of sky that you can observe
Celestial objects are observable objects like stars, planets, etc.

6. Motions of Celestial Objects
2. An arc is the motion that a celestial object moves across the sky
3. Polaris does not appear to move, therefore has no arc
a. The closer an object is to Polaris the smaller is the arc
Starry Night

7. Motions of Celestial Objects
The celestial objects that arc across the sky appear to rise in the East and set in the West
b. Except for celestial objects close to Polaris which appear to revolve around Polaris
c. Also except for the planets which appear to “wander”, sometimes moving East to West, sometimes moving West to East, and sometimes appearing to stand still = Retrograde Motion

8. Retrograde Motion “apparent” motion that objects are moving backwards
Farther from the sun because orbital velocities are slower

11. Apparent Motion of Celestial Objects at the North Pole and Equator
0o - equator
Earth’s axis

12. Motions of Celestial Objects
All celestial objects, including our moon and sun, appear to move 15o/hr
If an arc was 60o long, how many hours of time is that?

13. Apparent Motion of Celestial Objects at our Latitude
Earth’s axis of Rotation
Our latitude – 42o N

14. ROTATION Spinning of an object on it’s axis
Earth spins counterclockwise looking down on North Pole

15. Evidence of Earth’s Rotation
Star Trails –
If took a picture with the aperture open, you would get a 15o arc of the star “moving”
- Stars appear to mover 15o/hr around Polaris

17. 2. Foucault Pendulum
As the Earth rotates under the pendulum, the pendulum appears to gradually shift the direction of swing.

19. 3. Coriolis effect
Causes of winds and oceans currents to be deflected to the right in the northern hemisphere and to the left in the southern hemisphere.

21. 4. Day and Night

23. If Earth did not rotate, there would be no evidence shown above!!

24. Revolution Movement around an object
Earth revolves _____________ around the sun
Evidence
1. Changing Constellations - Seasonal changes in apparent positions of constellations
2. Seasons
Counterclockwise (CCW)

25. The constellations we see change throughout the year
WHY???

26. Big Dipper Revolving Around Polaris in 24 hours