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