Celestial Objects and Motions What keeps objects in

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 Dynamic equilibrium 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 = Earth Did not explain retrograde motions of some planets

PLANETARY MOTION Models 2. 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

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Apparent Motion of Celestial Objects at the North Pole and Equator 90 o N 0 o - equator Earth’s axis

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

Apparent Motion of Celestial Objects at our Latitude Earth’s axis of Rotation Our latitude – 42 o 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 15 o arc of the star “moving” - Stars appear to mover 15 o/hr around Polaris

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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=XJc 1 dn b. VK_0 • http: //www. google. com/doodles/leonfoucaults-194 th-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=mc. Ps_ Od. QOYU

4. Day and Night

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

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

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

Big Dipper Revolving Around Polaris in 24 hours

• http: //www. onr. navy. mil/Focus/spacescien ces/observingsky/constellations 3. htm http: //ecuip. lib. uchicago. edu/diglib/science/cultural_astronomy/inter actives/polaris. swf