1. The Reasons for Seasons. 1
The Reasons for Seasons? 1. Is it due to changes in the distance between the earth and the sun? OR 2. Is it due to the tilt of Earth’s axis?
Copyright 2005 by the Rector and Visitors of the University of Virginia
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The Seasons

2. Rotation vs. Revolution
Rotation is the spin of the Earth around its axis.
The Earth rotates once a day (every 24 hours).
Revolution is the orbit of one object around another.
The Earth revolves around the Sun every 365 and quarter days.
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3. Day Night Cycle is due to Earth’s rotation or spinning at its axis.
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4. Tilt of the Earth’s Axis
Tilt: A sloping position or movement.
Axis of Earth: An imaginary line that passes through Earth’s center and the North and South poles, about which Earth rotates.
The axis around which the Earth rotates is tilted by 23.5 degrees
This is what causes seasons.
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6. Tilt of the Earth’s Axis
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7. Seasons
Places away from the Earth’s equator & poles experience all four seasons: winter, spring, summer, and autumn.
Places near the Earth’s equator & poles does not experience all seasons.
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8. How Sunlight Hits Earth
Near the equator
Near the equator, sunlight hits Earth’s surface from almost overhead.
At the equator, sunlight is concentrated over smaller area, therefore, that area gets more heated up
Near the poles
Near the poles, sunlight arrives at steep (lower) angle.
Sunlight is spread out over a greater area.
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10. Equinoxes and Solstices
The Vernal (Spring) Equinox (March) Equal day and night
The Summer Solstice (June)
Longest day of the year
The Autumnal (Fall) Equinox (Sept.) Equal day and night
The Winter Solstice (December) Shortest day of the year
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11. Solstices
The sun appears farthest north of the equator once each year and farthest south once each year.
When farthest north of the equator – summer solstice in Northern Hemisphere & winter solstice in Southern Hemisphere
This occurs around 21 June
Longest day in the Northern Hemisphere & shortest day in Southern Hemisphere
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12. Solstices
When farthest south of the equator – summer solstice in Southern Hemisphere & winter solstice in Northern Hemisphere
This occurs around 21 December
Longest day in the Southern Hemisphere & shortest day in Northern Hemisphere
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13. Equinoxes
Halfway between the solstices, neither hemisphere is tilted towards the sun.
Day and night are equal, each are about 12 hours long everywhere.
This occurs around March 21
Vernal (spring) equinox in Northern Hemisphere & autumnal (fall) equinox in Southern Hemisphere
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14. Equinoxes This occurs around September 22
Vernal (spring) equinox in Southern Hemisphere & autumnal (fall) equinox in Northern Hemisphere
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15. Seasons Misconception
Many people think that the seasons are due to the distance of the Earth from the Sun. However:
The Earth’s orbit around the Sun is nearly a perfect circle. The Earth is slightly closer to the Sun in January and farther from the Sun in July.
If the seasons were due to our distance from the Sun both hemispheres would have the same seasons at the same time.
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16. The Seasons
In fact, the seasons are due to the tilt of the Earth’s axis. Consider what happens on June 21 when the northern hemisphere of the Earth is tilted toward the Sun:
The sunlight strikes the ground more vertically than in December. The light is spread out over less ground and heats the ground better.
The Sun is above the horizon for a longer period of time.
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17. A.M. and P.M. At midday, the Sun is on your meridian.
This occurs close to, or at, noon.
A.M. comes from ante meridiem (Latin) (before midday)
P.M. comes from post meridiem (Latin) (after midday)
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18. Daylight Saving Time
During the late spring, summer, and early fall, we set out clocks ahead to have an extra hour of daylight at the end of the day.
This change in time is called Daylight Saving Time.
The idea of changing our clocks was first used in the United States during World War I to conserve energy.
Since 1986, the United States has set our clocks one hour ahead on the first Sunday in April and one hour behind on the last Sunday in October.
Spring ahead, fall back.
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19. animations Seasons use code cfp-5012
Cosmic Map

20. Now, see what you know about the seasons!

21. Exit ticket 1. What are solstices and equinoxes?
2. How are they related to the seasons?

22. QUIZ TIME
1. Write answers in complete sentences for open ended questions.
2. If you draw pictures and MUST label them.
3. When done, review your questions and answers again.
4. After reviewing, put your quiz in your folder.
5. Start reading pages in the text book.

23. 1. Write a detailed paragraph describing the changes that take place each season in Atlanta.
2. Explain how seasonal changes in temperature and hours of daylight relate to changes in Earth’s position as it moves around the sun.

24. June
Northern hemisphere
Direct sunlight rays overhead and more hours of sunlight
Summer
Southern hemisphere
Sun’s energy is spread over large area and less hours of sunlight
Winter