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 hoursSpeed 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)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 DayThe time it takes the Earth to

rotate once with respect to a reference star.

One 360° RotationTime = 23 hr. 56 min. 1-2: Globe rotates 360° - sidereal

1-3: Globe re-points to sun - synodic

Evidence of Rotation

Foucault PendulumThe 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 precessionmoves opposite to itsrotation.

Earth’s axis will not straightendue to its constant rotation.

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