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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
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