The Seasons
Five Physical Factors That Produce Seasons:
1. Revolution
2. Rotation
3. Tilt*
4. Axis
5. Sphericity
Revolution
A. Elliptical
B. 93,000,000 miles from Earth
• perihelion
• Aphelion
C. One revolution = 1 year
• 365 ¼ rotations on axis in time it takes
to make one revolution
• Too difficult to deal with fractions, so
every 4 years we have a leap year
(Feb. 29)
Rotation
A.
B.
C.
D.
E.
F.
One complete turn in 24 hours
Turns eastward
Angular velocity; constant 360 degrees
Linear Velocity; distance covered in 24 hours
Accounts for day/night
Unaware of speed b/c no reference point
Tilt*
• Axis is aligned at a 23.5 degree angle
perpendicular to the plane of earth's orbit
Axis
•Remains in a fixed alignment of axial parallelism
•Earth's axis relative to the palne of the elliptic
does not change
Sphericity
• Appears as a n oblate spheroid to the
Sun’s parallel rays
Inclination
• Summer Solstice
– June 21
– Northern Hem receives more sunlight
– North of the Artic Circle receives 24 hours of
daylight
• Equinox (Autumnal)
– September 22
– Day and night will be equal in all places
• Winter Solstice
– December 21
– North of Artic Circle will get 24 hrs of night
• Vernal Equinox
– March 21
– Days and nights will be equal
Lines on Earth and Solar Energy
• Angle of inclination is important to how
much energy the Earth receives from the
sun
• Global reference points
– Arctic Circle (66 ½ °N)
– Antarctic Circle (66 ½ °S)
– Tropic of Cancer (23 ½°N)
– Tropic of Capricorn (23 ½ °S)
Insolation
• Season variation in temp is a result of
• Causes of changes in insolation
– Atmosphere
– Duration of daylight
– Angle of solar rays
The Seasons Demo
http://www.ioncmaste.ca/homepage/resources/web_resources/CSA_Astro9/file
s/multimedia/unit3/reasons_seasons/reasons_seasons.swf