Earth and Season

Earth’s Circumference

• Erastosthenes determined the earth’s

circumference was 46,250 km

• At the equator = 40,074 km
• At the poles = 40,007 km

Earth’s Shape

• Oblate spheroid
• Spherical: slightly

flattened at the poles
and bulges at the
equator.

• As Earth rotates, the

sphere is distorted by
centrifugal force.
– Causes objects to move

outwards from the
center

– Greatest at the equator

Axis

• An imaginary line that runs through the

earth from the north pole to the south
pole.

• The earth rotates (spins) on its axis.

Tilt

• The earth is tilted at

23.5°

Coordinate system- a system of intersecting lines
used to determine locations on the Earth’s surface

Latitude

• Latitude: Measures distance North and South

of the Equator

• Parallels: imaginary lines that run E to W

Longitude

• Longitude: Measures distance in degrees east

and west of the Prime Meridian.

• Meridians: lines of longitude

Earth’s Movement

• Rotation: spinning

motion of the earth.
24 hours for one
rotation (1 day).

• Revolution:

movement of the
earth around the sun.
365 1/4 days (1 year)

EARTH 'Movement Part 2

• Precession:The slight movement of Earth’s

axis over 26,000 years.

• Diurnal motion of stars: It is the motion of

the sky due to Earth's daily rotation. Stars
and other celestial bodies appear to move
from east to west. The axis of this apparent
motion coincides with Earth's axis of rotation.

•

Earth’s Movement Part 3

•Nutation

•–the wobble

•Change in the angle of the axis (1/2 degree)

Barycenter
•The point between two objects where they balance each other.

Reason #1: # of daylight hours

• The amount of sunlight varies throughout the

year. The tilt of the earth means no two
latitudes get the same amount each day.

• In the summer you have more hours of

sunlight and fewer in the winter.

Reason #2: Angle of sunlight

• The angle of the sun’s rays cause different

intensities, this is also caused by the tilt of the
earth.

Equinoxes

• Vernal Equinox: March 21-22
• Autumnal Equinox: Sept. 21-22
• 12 hours of daylight/12 hours of darkness
• The sun is directly overhead at the equator

Solstices

• Summer Solstice

– June 21-22
– Longest day of the year in the N. Hemisphere
– The sun is directly overhead at the Tropic of

Cancer.

• Winter Solstice

– December 21-22
– Shortest day of the year in the N. Hemisphere
– The sun is directly overhead at the Tropic of

Capricorn.