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Celestial Objects and Motions
What keeps objects in orbit?
Gravity -
Inertia
Dynamic equilibrium
the force that attracts a body toward the center of any other
physical body having mass.
property of matter by which it continues in its uniform motion in a straight line
PLANETARY MOTION Models
1. Geocentric Model (Aristotle) – earth centered
Geo = EarthDid not explainretrogrademotions of some planets
PLANETARY MOTION Models
2. Heliocentric (Copernicus) – Sun centered
Helio = Sun
Everything revolves aroundthe 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.
2. An arc is the motion that a celestial object moves across the sky
3. Polaris does not appear to move, therefore has no arca. The closer an object is
to Polaris the smaller is the arc
Motions of Celestial Objects
Starry Night
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
Motions of Celestial Objects
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
Earth’s axis
90o N 0o - equator
• All celestial objects, including our moon and sun, appear to move 15o/hr
Motions of Celestial Objects
• 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
1. 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 As the Earth rotates under the pendulum, the
pendulum appears to gradually shift the direction pendulum appears to gradually shift the direction of swing.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???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