Transcript Actual Earth Motions

Actual Earth Motions
Rotation
The Earth spins upon an
imaginary line that runs
through the planet from
the North to South pole
known as an axis.
The Earth’s axis is
tilted 23 ½ ° from
perpendicular.
The Earth rotates at a
rate of 15° per hour
from west to east.
The Foucault
Pendulum
Evidence of
Rotation
The Foucault
pendulum when
swinging freely will
move in a
predictable way.
The pendulum
“appears” to move in
clockwise fashion over
time. In reality, the
Earth is rotating
underneath the
pendulum making the
pendulum “appear” to
shift position over
time.
The Foucault
Pendulum
The Coriolis
Effect
Evidence of
Rotation
The tendency of objects to veer
away from a straight-line path
is known as the Coriolis Effect.
Objects tend to veer to the right in
the Northern Hemisphere and to
the left in the Southern
Hemisphere.
This “deflection” of an object from a
straight-line path is due to the rotation of
the Earth underneath an object set into
motion.
The object “appears” to veer or be
deflected from its original target. In fact,
the target has changed its position due to
the Earth’s rotation.
The Coriolis
Effect
The Coriolis
Effect
Evidence of the Coriolis
Effect can be seen in
global pattern of winds,
large storms and ocean
currents.
Revolution
The Earth moves around the Sun
once a year (365 ¼ days) –
roughly at a rate of 1° per day.
Evidence of
Revolution
Change in
Constellations
A constellation is a group of stars
that form a pattern in the sky.
Throughout the year different
constellations can only be observed
during different seasons.
Evidence of
Revolution
Seasonal
Change
The seasons we experience on our
planet are a result of the revolution
of the Earth around the Sun and the
23 ½ ° tilt of the Earth’s axis.
Because of the Earth’s tilt, areas of
the planet receive varying amounts
of sunlight throughout the year –
leading to seasonal change.
Evidence of
Revolution
Change in Sun’s
Diameter
The Earth’s orbit around the
Sun is slightly elliptical. The
Earth at one point in its
revolution is closer to the
sun (perihelion). The Earth is
furthest from the sun at
aphelion.
The Sun’s apparent diameter
seems to change as the earth
revolves around the Sun
(Larger in perihelion; smaller
in aphelion).
Evidence of
Revolution
Doppler Effect
of Stars
As the Earth revolves around
the Sun, it will travels towards
a particular star one half of the
year and travel away from it
the second half of the year.
Movements “to and from” stars
can be seen as slight “blue and
red” shifts in starlight.
Earth’s Motions and
Time
Local Time: Time based on rotation of the Earth reflected in
“apparent” motions of the Sun.
Solar Noon: The time of the day when the Sun reaches its
highest altitude in the sky.
Solar Day: The time it takes the Earth to rotate from one solar
noon to the next solar noon.
Mean Solar Day: Average rate at which the Earth rotates from
one solar noon to the next.
Mean Solar Time: 24 hours = 1 day!
Time Zones: 15° wide bands of meridians established to
reflect mean solar time.