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
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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