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#18 The Reason for the
Seasons
(Tilting towards summer!)
A Review:
orbit – the elliptical path of motion a body takes
as it travels around another body in space
 Light year – the distance light can travel in a
year (9.5 trillion km or 5.88 trillion miles / year - that’s 12 “0”s!!!)
Just for Interest:
 Light travels about 300,000 km (186,000 miles)
per second
 The North Star is 431 light years from Earth
 Our nearest star, Proxima Centauri, is 4.28 lightyears away

Rotation vs. Revolution

rotation – the spinning motion of a body
on its own axis
(24 hr for Earth)

revolution – the elliptical motion of a body
as it orbits another body in space

period of revolution – the time it takes to
make one complete orbit, or revolution
(roughly 365 days for Earth)
Quick quiz....
What causes us to have day and night?
Is the rotation or the revolution of the Earth?
What About The Seasons?

Seasons are
caused by
the tilt of
the Earth

When it is summer in San Diego
County, the north pole of the
Earth is tilted toward the sun.

When it is winter in San Diego County, the
north pole is tilted
away
from the sun.
Draw this next slide
REALLY BIG
– it’s the last thing going in your
notes for today
(Use the next page in your spiral
if you have to.)
Be sure to label EVERYTHING!
Want a moving rendition?
Click on this Demo!
(This will work at home, but not here at school)