Seasons on Earth

1
Seasons on Earth

• All Figures from
• http//www.fourmilab.ch/earthview/vplanet.html

By Diana L. Duckworth Rustburg High
School Campbell County, VA
2
Three Factors Cause Seasons

• Tilt of Earth at 23.5 degrees latitude
• Greater tilt - more extreme seasons
• Less tilt - less extreme seasons
• Revolution of Earth around Sun
• Elliptical orbit
• Perihelion - January
• Aphelion - July
• Parallelism of Axis of Rotation
• Axis always points toward Polaris

3
Tilt of Axis

• Causes sun to be directly overhead at a different
  latitude each day
• Summer Solstice _at_ 23.5N (June 21)
• More daylight more intense radiation in
  Northern Hemisphere
• Winter Solstice _at_ 23.5S (December 21)
• More daylight and more intense radiation in
  Southern Hemisphere
• Equinox (twice a year) _at_ Equator
• Days Nights are 12 hours each everywhere

4
Key to Figures

• In the following illustrations, the dark area
  represents the 50 of the earth that is in
  darkness and the light areas represent the 50 of
  the earth that is in daylight.
• In all figures, the sun can be considered to be
  in the geographic center of the image.

5
Equinox 0Z
6
Equinox 3Z
7
Equinox 6Z
8
Equinox 9 Z
9
Equinox 12Z
10
Equinox 15 Z
11
Equinox 18Z
12
Equinox 21Z
13
Equinox 24Z
14
Summer Solstice 0Z
15
Summer Solstice 3Z
16
Summer Solstice 6Z
17
Summer Solstice 9Z
18
Summer Solstice 12Z
19
Summer Solstice 15Z
20
Summer Solstice 18Z
21
Summer Solstice 21Z
22
Summer Solstice 24Z
23
Winter Solstice 0Z
24
Winter Solstice 3Z
25
Winter Solstice 6Z
26
Winter Solstice 9Z
27
Winter Solstice 12Z
28
Winter Solstice 15Z
29
Winter Solstice 18Z
30
Winter Solstice 21Z
31
Winter Solstice 24Z
32
Tilt of Axis Locates Key Latitudes

• Tropic of Cancer - where Suns rays are vertical
  at Summer Solstice tilt 23.5N
• Tropic of Capricorn - where Suns rays are
  vertical at Winter Solsltice tilt 23.5S
• Arctic Circle - latitude of total daylight at
  Summer Solstice or darkness at Winter Solstice
• 90 - tilt 90N - 23.5N 66.5N
• Antarctic Circle - latitude of total daylight at
  Winter Solstice or darkness at Summer Solstice
• 90 - tilt 90S - 23.5S 66.5S

33
(No Transcript)
34
7 AM Nov 7, 2004 Sun _at_ 1628 S
35
Winter Solstice view from Sun
36
Equinox view from Sun
37
Summer Solstice view from Sun
38
Summer Solstice view from Moon
39
Equinoxview from Moon
40
Winter Solstice view from Moon
41
As the World Turns

• Rotation has nothing to do with seasons!

42
(No Transcript)
43
(No Transcript)
44
(No Transcript)
45
(No Transcript)
46
(No Transcript)
47
(No Transcript)
48
(No Transcript)
49
Changes with the Seasons

• Maximum elevation of sun position in sky from
  Northern Hemisphere
• June to December - gets lower farther to South
• December to June - gets higher farther to North
• Length of Daylight
• June to December - daylight gets shorter
• December to June - daylight gets longer