Movements of the Earth:
Rotation and the Effects
By: Myra C. Beltran
III-6 BEED
Movements of the Earth
The earth has three basic movements:
1.) galactic movement
2.) rotation
3.) revolution
The Other two Movements of the Earth:
1.) rotation on an axis
2.) revolution around the sun
(vital interest of the geographers)
The Consequences of these Movements are:
1.) the phenomena of day and night
2.) variations in the length of day
3.) and the changing seasons
Rotation
-Refers to the turning of the earth on its own
axis, an imaginary line extending from the North Pole to
the South Pole.
For points along the equator such as:
Kampala, Uganda – the velocity is about 1500 feet per
second, or approximately 1050 miles/ 1680 km per
hour.
In comparison, at Leningrad, USSR, where the earth
rotates about 525 miles per hour.
We are unaware of the speed of rotation:
1.) the rate is constant for each place on the earth’s
surface
2.) the atmosphere rotates with the earth
3.) there are no nearby objects, either stationary or
moving at a different rate with respect to the earth.
How do we know that the Earth rotates?
1. ) Star trails- trails made with time exposure, circular
paths that occur because the planet is moving and not
stationary.
2. ) Winds curve because of the Earth’s rotation.
3. ) Ocean currents curve clockwise in the northern
hemisphere, and counterclockwise in the southern
hemisphere.
4. ) The movement of a pendulum. It does not actually
move, it is the Earth moving that causes the pendulum
to appear to change the direction of its swing.
The earth turns in an EASTWARD direction.
Rotation accounts for our alternating days and nights.
The line around the earth separating the light and dark
halves is known as the CIRCLE OF ILLUMINATION.
Revolution
-While the earth rotates on its axis, it also
revolves around the sun in an elliptical almost circular.
It rotates toward the morning sun (that is, toward the
east).
This eastward direction of rotation not only defines the
movement of the zone of daylight on the earth’s
surface, but also helps define the circulatory
movements of the atmosphere and oceans.
Ellipse
The velocity of rotation on the earth varies depending
on the distance of given place from EQUATOR.
The Earth’s orbit around the sun is NOT a perfect circle.
It is an ellipse.
The rotational velocity at the poles is nearly zero.
Orbit at an average distance from the sun of about
93,000,000 miles.
The greatest velocity of rotation is found at the equator.
In addition to a constant angle of inclination, the earth’s
axis maintains another characteristic called
PARALLELISM.
Perihelion (from the Greek word: peri, close; helios,
sun) it’s distance then from the sun is approximately
91,500,000 miles.
Aphelion (Greek: ap, away; helios, sun); its distance is
about 94,500,000 miles from the sun.
The period of time the earth take to make one
revolution around the sun determines the length of one
year.
The Seasons:
Why do we have seasons?
1.)Seasons are the result of the tilt of the Earth's axis.
2.) Earth’s axis is tilted 23.5°.
3.) This tilting is why we have SEASONS like fall, winter,
spring, summer.
4.) The number of daylight hours is greater for the
hemisphere, or half of Earth, that is tilted toward the
Sun.
Summer is warmer than winter (in each hemisphere)
because the Sun's rays hit the Earth at a more direct
angle during summer than during winter
Because the earth makes 365 ¼ rotations on its axis
during the time it takes to complete on revolution of
the sun, a year is said to have 365 ¼ days.
Also the days are much longer than the nights during
the summer.
It has been decided that a year would have 365 days
and that in every fourth year, called LEAP YEAR; an
extra day would be added in February.
During the winter, the Sun's rays hit the Earth at an
extreme angle, and the days are very short. These
effects are due to the tilt of the Earth's axis.
Plane of the Ecliptic, Inclination, and Parallelism:
The earth in its orbit around the sun moves in a
constant plane. This plane is called PLANE OF ECLIPTIC.
The earth’s axis is titled at an angle of 23 ½˚ from the
vertical to the plane of the ecliptic and thus has a
constant ANGLE OF INCLINATION, as it is called, of 66½˚
with the plane.
Solstices occur twice a year, when the tilt of the Earth's
axis is oriented directly towards or away from the Sun,
causing the Sun to appear to reach its northernmost
and southernmost extremes.
Winter solstice is the shortest day of the year. In the
Northern Hemisphere. It occurs on December 21 and
marks the beginning of winter.
The Summer Solstice is the longest day of the year. It
occurs on June 21 and marks the beginning of
summer.
During the winter the Northern Hemisphere day lasts
fewer than 12 hours and the Southern Hemisphere day
lasts more than 12 hours.
During the winter solstice, the North Pole has a 24-hour
night and the South Pole has a 24-hour day.
Sunlight strikes the earth most directly at the Tropic of
Capricorn.
Equinoxes
A day lasts 12 hours and a night lasts 12 hours at all
latitudes.
Equinox literally means "equal night".
Sunlight strikes the earth most directly at the equator.
This occurs twice a year.
The Earth's seasons are not caused by the differences
in the distance from the Sun throughout the year.