Download Earth

Geocentric/Heliocentric
Models to Explain Motion
• Geocentric Model – Earth centered.
–Planets, stars, and other objects
revolve around Earth.
• This model was able to explain the
apparent motion of the stars, sun, and
moon.
–Could not explain retrograde motion
and foucault pendulum motion.
Retrograde Motion
• Retrograde motion is an apparent
motion of planets (over weeks to
months) when they appear to
change position with respect to
the background field of stars.
Retrograde Motion Cont…
• Retrograde motion is caused by
Earth and other planets
revolution around the Sun in
different orbits at different
speeds.
Retrograde Motion of the Planets
http://www.flex.com/~jai/astrology/retrograde.html
Models to Explain Motion
• Heliocentric Model – Sun centered.
–Earth rotates on an imaginary axis and
revolves around the Sun.
• The Moon revolves around Earth.
–Explained all of the observations made
by the scientists including retrograde
motion.
Actual Earth Motion
Rotation – Earth spins on its axis from
west to east at 15 degrees per hour.
• The Sun, Moon, stars appears to move
across the sky at a rate of 15 degrees per
hour.
• The Foucault pendulum and the Coriolis
Effect confirm Earth’s rotation.
Foucault Pendulum
• A pendulum is a freely swinging weight.
• Over a day, the direction of motion of a
pendulum will appear to change.
Actually, Earth is rotating under the
pendulum.
Coriolis Effect
• Coriolis Effect - the bending of winds
and currents due to the rotation of Earth.
• Northern Hemisphere, they bend to the
right.
• Southern Hemisphere, they bend to the
left.
Earth’s Revolution
• Earth revolves around the Sun once a year.
– It revolves approx. 1° per day.
• Earth is closest to the Sun on January 3rd.
This is called the perihelion.
• Earth is farthest to the Sun on July 3rd. This is
called the aphelion.
• Evidence of revolution
– Seasons
– Different constellations throughout the year.
http://www.onr.navy.mil/focus/spacesciences/observingsky/sun2.htm