Earth’s Motions

ROTATION Earth spinning on its axis is called rotation. The “AXIS” is an imaginary line passing through Earth’s center through the N. and S. Pole. The N. Pole points toward the star Polaris The axis is tilted 23.5° {ch.2}

DAY AND NIGHT Counterclockwise rotation (In N. Hemisphere)! Sun (Celestial Sphere; stars) rise in the East and set in the West. Time of Complete Rotation = ~24 hours Speed at Equator = ~1 mile every 3 seconds = 1,038 miles per hour {Ch.1}

Oblate Spheroid Earth’s shape is considered to be the shape of an ellipsoid. Earth is wider than it is tall. Bulges at equator Flattened at Poles.

Solar vs. Sidereal Solar Day (SYNODIC) Sidereal Day The time it takes Earth to rotate once with respect to the sun. (Suns Highest point in sky to the next highest point in sky). Time = 24 hours (mean time) Sidereal Day The time it takes the Earth to rotate once with respect to a reference star. One 360° Rotation Time = 23 hr. 56 min. 1-2: Globe rotates 360° - sidereal 1-3: Globe re-points to sun - synodic

Evidence of Rotation Foucault Pendulum The pendulum is suspended above Earth’s Surface. The Earth spins underneath pendulum. Pendulum seems to change direction because rotation. (ch.8)

Precession The slow gyration of a spinning body. Movement around a point or axis. The top does not fall over as long as it stays spinning.

Earth’s Precession The Earth “WOBBLES” on its axis once every 26,000 years. Earths precession moves opposite to its rotation. Earth’s axis will not straighten due to its constant

Moving Toward VEGA

Revolution The movement of one object around another is called revolution. Earth revolves around the sun in a path called its orbit (Counterclockwise direction). 1 revolution = 365.25 Days (LEAP YEAR?) Rate of Revolution = 66.000 mph