Earth’s Position in Space and seasonal changes
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Transcript Earth’s Position in Space and seasonal changes
Earth’s Position in Space
and Seasonal Changes
Earth orbits around the Sun
1 revolution (orbit) = 1 year (365 days and 6
hours)
http://www.classzone.com/books/earth_scienc
e/terc/content/visualizations/es0408/es0408p
age01.cfm?chapter_no=04
Earth rotates on its axis
Axis = imaginary vertical line around
which Earth spins
Earth rotates East to West
(counterclockwise)
Rotation of Earth makes Sun appear to
move in sky
Sun comes into view on Eastern horizon
and sets on Western horizon
One rotation = around 24 hours
Earth’s orbit is an
ellipse, not
perfectly round
(flattened circle)
Sun is not in
center but slightly to one side
Sun is closest to Earth around Jan 3
Sun is farthest from Earth around July 4
Obviously, the distance from Earth to Sun does
not cause our seasonal changes
Why do seasonal changes occur?
The amount of solar radiation received on Earth
varies
Earth’s axis is tilted 23.5°
Tilt cause different parts of the Earth to receive more
solar radiation than others
Annual variation in incoming solar radiation
For example: In summer, rays hit more directly, are at a
higher angle for a longer period of time
Different hemispheres receive more solar radiation at
different times of the year
Summer occurs in hemisphere tilted toward Sun,
winter in hemisphere receiving less radiation
Here Comes the Sun!
Solstice
Occurs when Sun’s rays reach
greatest distance North or South
of equator
Each hemisphere has a Winter
and a Summer Solstice
In the Northern Hemisphere
Winter Solstice occurs:
Dec 21 or 22
Sun rays directly over
Tropic of Capricorn
Sun rises in Southeast
and sets in Southwest
Sun appears lowest in sky
Days are shortest
Summer Solstice In Northern
Hemisphere
June 21 or 22
Sun rays hit directly on
the Tropic of Cancer
Sun rises in Northeast and
Sets in North west
Sun appears highest to
us in sky
Sun would appear directly
overhead at Tropic of
Cancer
Days are much longer
Remember: The Sun is Never
Directly Overhead In Most of the
Northern Hemisphere
Equinoxes: Sun’s rays hit directly
on equator
Number of daylight hours will equal the
number of nighttime hours all over the
world
Neither Hemisphere is tilted to the Sun
Each hemisphere has a spring and a fall
equinox
In Northern Hemisphere
Spring equinox = March 20 or 21
Fall equinox = Sept 22 or 23