24.2 Sun and Seasons
http://highered.mcgrawhill.com/sites/007299181x/student_view0/cha
pter2/seasons_interactive.html
Earth Motions
1. Earth moves in two major ways:
– Rotation: spinning of earth on its axis
– Revolution: earth orbits around the sun
What Causes Seasons?
1. Tilt of the earth as it moves around the sun
- Earth is tilted by 23.5 degrees
2. As the earth orbits, different parts of the
earth get direct and intense solar radiation
Seasons
3. Opposite in the N and S hemisphere
4. When N tilted to the sun (summer), S tilted
away (winter)
5. If the earth was not tilted= no seasons
Seasons and Latitudes
1. Polar: Cold, don’t have 4 seasons
– (66.4 N or S to poles)
2. Temperate: 4 seasons (23.5-66.5 N or S)
3. Tropics: Warm all year, no seasons (23.5 N or S)
– Get intense rays all year long
• Solstice: sun is directly overhead at latitude
23.5 N or S
• Equinox: neither hemisphere is tilted toward
the sun, and the lengths of daylight and
darkness are =
VERNAL EQUINOX : March 21
1st day of spring
Days get longer and warmer
Sun’s direct & intense rays fall on the EQUATOR (and move north throughout spring)
(equal day and night @ equator)
SUMMER SOLSTICE: June 21
1ST day of SUMMER
Longest day of the year – Shortest night
Sun’s direct & intense rays are over 23.5 N (Tropic of Cancer)
AUTUMNAL EQUINOX: Sept 23
1st day of Fall
Sun’s direct & intense rays fall on the EQUATOR
Days get cooler and shorter
(equal day and night @ equator)
WINTER SOLSTICE: Dec 21
1ST day of Winter
Longest night – shortest day
Sun’s direct & intense rays are over 23.5 S (Tropic of Capricorn)