What causes the seasons?

Essential Question: How does the Earth’s motion explain what we observe in the changing seasons?

During which months is Earth closest to the sun? Farthest from the sun? Closest in the winter months, farther in summer months http://www.classzone.com/books/earth_science/terc/content/investigations/es2603/es2603page01.cfm

So…. Does our distance from the Sun cause the seasons?? Aphelion -- on its orbit, when the Earth is farthest Away from the sun Perihelion -- the point on its orbit when the Earth is closest to the sun Farther Away closer July 4 summer January 2 winter So…. Does our distance from the Sun cause the seasons??

NORTH exactly SOUTH EXACTLY of E-W E-W of E-W E- W 14 h 15 m 12 9 h 8 m 12 72.6° 49.2° 25.7° 49.7° 70° 65° 27° 39° NORTH exactly SOUTH EXACTLY of E-W E-W of E-W E- W Collect data Short med long med. http://astro.unl.edu/naap/motion3/animations/sunmotions.html

Subtract to find out how much the Earth tilts on its axis Subtract to find out how much the Earth tilts on its axis. What pattern do you observe? Date Altitude (degrees) Difference in Altitude (degrees) June 21   September 21 December 21 March 21 Average of the differences in altitude (degrees) 72.6° 49.2° 23.4 The Sun’s angle in the sky varies 23.5 degrees from season to season because the Earth is TILTED 23.5 degrees! 23.5°

Factors are MAX in June, LOWEST in Dec Factors are MAX in June, LOWEST in Dec. and the EQUAL (except temp) in March and Sept. How soes Earth’s motion explain this?

Summer Fall Spring Winter Description: The figure below shows the Earth in its nearly (but not quite) circular orbit around the Sun, and the Earth-Sun distance for each season. Remind them that seasons are NOT caused by Earth’s changing distance to the Sun Ranking Instructions: For a person in the Northern Hemisphere, rank the Earth-Sun distance (from greatest to least) by season. (Use season names.) Ranking Order: Greatest distance 1 __________ 2 __________ 3 __________ 4 ___________ Least distance Summer Fall Spring Winter

On Earth, we OBSERVE the sun and moon rise/set at an ANGLE in the sky On Earth, we OBSERVE the sun and moon rise/set at an ANGLE in the sky. The Milky Way is at an ANGLE in the sky.

What about the Earth’s motion accounts for what you observe in this Video of the Land of the Midnight /Sun http://www.youtube.com/watch?v=HO91qdyqtj8

Why does the height of the Sun in the sky changes throughout the year? Zodiac constellations are at an ANGLE, so it the path of the Sun.

The Earth is tilted on its axis at 23 The Earth is tilted on its axis at 23.5 degrees – Does the direction of the tilt change? As earth orbits around the Sun, It tilts toward the Sun or it tilts away from the Sun.

As Earth orbits, it tilts 23. 5° TOWARD the Sun or 23 As Earth orbits, it tilts 23.5° TOWARD the Sun or 23.5°AWAY from the Sun away toward Run the animation to show that no matter where Earth is in its orbit around the Sun, it always tilts the SAME direction (toward Polaris) http://esminfo.prenhall.com/science/geoanimations/animations/01_EarthSun_E2.html

If the Earth did NOT TILT as it rotated on its orbit every 24 hours, Would the seasons change? Would there even be seasons? Describe the hours of daylight, angle of Sun, temperature, direction of sunrise/set Hrs. of daylight: 12 everywhere. Angle of Sun: always 90 at the equator, 23.5  at the Arctic Circle and always the same at each latitude. Sun would always rise in East and set in west.

Demonstrate Earth’s rotation WITHOUT tilt to see that hrs of daylight, temperature do not change http://www.sepuplhs.org/students/iaes/simulations/SEPUP_Seasons_Interactive.swf

Due to the curve of the Earth’s surface, The Sun’s Angle is different at different latitudes So… different locations receive different INTENSTIY of solar energy. The angle of solar energy is more dramatic when the Earth is tilted 23.5 degrees!

Tilt of the other planets Based upon the tilt, which planets would have no change of seasons? Mercury, Venus, Jupiter.

A. Ranking Instructions: Rank the time (from longest to shortest) that each location spends in daylight during the 24 hour rotation period. Ranking Order: Longest time 1 _____ 2 _____ 3 _____ 4 _____ 5 _____ Shortest time B. Ranking Instructions: Imagine that at each location (indicated by an X”) a glass of water is warmed by equally bright sunlight during each 24 hour rotation period. Rank the temperatures (from coolest to hottest) of the glasses of water. Ranking Order: Coolest 1 _____ 2 _____ 3 _____ 4 _____ 5_____ Hottest E B C A D D A C B E

14 hrs. 52 min.

Summer Solstice, June 21 north pole tilting toward the Sun 24 hrs. daylight 23.5° North of the equator equator Tropic of Capricorn 24 hrs. night

Where is the “Land of the Midnight Sun”? http://www.youtube.com/watch?v=HO91qdyqtj8

9 hrs. 8 min. sunrises & set 23.5° south of E_W

Winter Solstice, Dec. 21 (North pole tiltting AWAY from the Sun) 24 hrs of night equator 23.5° South of the equator Tropic of Capricorn 24 hrs. of daylight

The sun rises exactly east and sets exactly west The sun rises exactly east and sets exactly west. There are equal hours of daylight and night. 12 hrs.

Vernal (spring) Equinox Autumnal (fall) Equinox Equator equal daylight: 12 hrs. equal night: 12 hrs.

Connect angle to intensity. A) D-B-A-C B) C-A-B-D

Connect flashlight to Earth’s curved surface Connect flashlight to Earth’s curved surface. A) D- C or A- B B) B – C or A – D C) D – C or A - B

How does Temperature relate to latitude and angle?

Ranking Order: Coolest 1 _____ 2 _____ 3_____ 4_____ 5_____ Hottest Connect ANGLE to INTENSITY to HOURS of daylight to TEMPERATURE. A) C-B-A-D-E (look at the length of dotted line in daylight) B) E- C – D – A – B Ranking Order: Coolest 1 _____ 2 _____ 3_____ 4_____ 5_____ Hottest

Summer days in Oswego are likely to be hotter than winter days because A. in summer Earth is closer to the Sun B. the number of sunspots increases C. Earth’s northern axis is tilted toward the Sun D. the Sun gives off more energy 2. To an observer in Oswego, Illinois, the North Star, Polaris, is always located above the northern horizon at an altitude of approximately A. 23½° B. 41° C. 66½° D. 90° 3. The height of the Sun in the sky changes with the seasons because A. Earth's axis is tilted B. Earth's distance from the Sun changes C. the Sun revolves D. the Sun rotates 4. In which direction on the horizon does the Sun appear to rise on June 21 in Illinois? A. due east B. north of due east C. south of due east On March 21st and September 21st, the hours of daylight in Oswego will be A. 0 B. 9 C. 12 D. 15 1. C 2. C. 12 3. A 4. B

5. Base your answers to this question on the diagram below, which shows the tilt of Earth on its axis in relation to the Sun on one particular day. Points A through E are locations on Earth’s surface. Point D is located in Chicago, IL. The dashed line represents Earth’s axis. Which diagram best represents the angle of the Sun’s rays received at location C at noon on this day? A B C D 6. On this day, which location has the greatest number of hours of daylight? A. B. C. D. E.

equator North Pole Directly overhead