Earth’s Motions

ROTATION

PRECESSION

REVOLUTION

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) 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

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

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