Transcript Grade Nine Science

Earth and Space Science
13.3 The Effects of Planetary
Motion
Earth’s Rotation
• The Earth rotates (spins) on an axis.
• It takes 24 hours to do one rotation around its axis.
• This motion causes most stars, sun and moon to
appear to rise in the east and set in the west.
• The Earth’s axis is an imaginary line that connects
the North Pole to the South Pole.
Earth’s Rotation
Revolution
• The planets revolve around the Sun in paths called
orbits.
• The orbits of most planets are nearly circular, with
the Sun at the center of each orbit.
• The period of time for one revolution around the sun
is called one orbital period.
Earth’s Revolution
• It takes Earth one year (365 days) to travel and
revolve in a circle around the sun.
• This allows us to see different stars and
constellations during different seasons.
• The angle of the Earth’s axis and the Earth’s
Revolution causes the different seasons.
Earth’s Seasons
• Earth rotates at a tilt of
23.5.
• During our summer
months, the northern
hemisphere is tilted
toward the Sun.
The Earth’s Seasons
Seasons
• http://www.youtube.com/watch?v=WLRA8
7TKXLM&feature=related
Seasons Video
Homework
• Read pg. 404 - 405
• Answer # 1 – 5 on pg. 405