Celestial Objects and Motions

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

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

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

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.

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

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

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

http://ed.ted.com/on/WAdUQ3Z3 http://www.youtube.com/watch?v=72FrZz_zJFU

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

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?

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

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

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

http://www.youtube.com/watch?v=awLEp--R4sA http://www.youtube.com/watch?v=f-iQxCRqw64 http://apod.nasa.gov/apod/ap060915.html

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

http://www.youtube.com/watch?v=XJc1dnbVK_0 http://www.google.com/doodles/leon-foucaults-194th-birthday

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.

http://www.youtube.com/watch?v=mcPs_OdQOYU

4. Day and Night

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

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)

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

Big Dipper Revolving Around Polaris in 24 hours

http://www.onr.navy.mil/Focus/spacesciences/observingsky/constellations3.htm http://ecuip.lib.uchicago.edu/diglib/science/cultural_astronomy/interactives/polaris/polaris.swf