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Seasons.

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Presentation on theme: "Seasons."— Presentation transcript:

1 Seasons

2 Reasons for the Seasons:
Tilt of Earth’s axis Axial parallelism Sphericity Axial parallelism: axis maintains alignment during orbit around sun (FIXED); North Pole points to Polaris (North Star)

3 Landmark dates ... December Solstice March Equinox June Solstice
September Equinox, September 22/23

4 Landmark latitudes ... Equator = 0o Tropic of Cancer = 23.5oN
Arctic Circle = 66.5oN Tropic of Capricorn = 23.5oS Antarctic Circle = 66.5oS

5 On each day,….. 1. What is subsolar point (SSP)?
SSP is latitude where sun is directly overhead; where sun’s rays are vertical. For each landmark date: answer these questions…

6

7

8 2. At what latitude will sun’s rays be oblique/tangent?

9

10 3. Where is Circle of Illumination?
separates light and dark halves

11

12 December Solstice 1.SSP? 23.5oS 2. tangent rays ? 66.5oN, 66.5oS
3. C.I. is tangent? at 66.5oN, 66.5oS

13 March Equinox 1.SSP? 0° 2. tangent rays? 90oN, 90oS
3. C.I. is tangent? at 90°N, 90°S

14 June Solstice SSP? 23.5oN 2. tangent rays? 66.5oN, 66.5oS
3. C.I. is tangent?

15 September Equinox 1.SSP? 0° 2. tangent rays ? 90oN, 90oS
3. C.I. is tangent? at 90°N, 90°S

16 Animated tour of the seasons

17 Annual March of the Seasons
What is range of SSP?

18

19 Angle of noon sun in a location=
90 - difference in degrees between latitude of location and SSP

20 Latitude?

21 Solution: Angle of noon sun (March 22) = 50 SSP (March 22) = 0 50 = 90 – (? – 0) ? = 40 for June 21: 73 = 90 – (?-23.5) ?-23.5 = 27 ? = 40.5

22 What is the angle of the noon sun in Duluth on September Equinox?
= 43 degrees

23 What is the angle of the noon sun in Duluth on December Solstice?
= 90 – 70.5 = 19.5 degrees

24 What is the angle of the noon sun in Duluth on June Solstice?
= 90 – (47N – 23.5 N) = 90 – 23.5 = 66.5 degrees

25 What is the angle of the noon sun in Duluth today (January 27)?
SSP today is approx. 20˚S. = 90 – (47N – 20 S) = 90 – 67 = 23 degrees


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