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The Reason for the Seasons EARTH’S TILT Length of Day – Angle of Rays.

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Presentation on theme: "The Reason for the Seasons EARTH’S TILT Length of Day – Angle of Rays."— Presentation transcript:

1 The Reason for the Seasons EARTH’S TILT Length of Day – Angle of Rays

2 Why do we have seasons?  Are the Seasons caused by the Earth being closer to or farther away from the sun?  NO Closer to the sun in January, and farther away in July.  Perihelion is the point along Earth’s orbit when Earth is closest to the Sun.  January  Aphelion is the point along Earth’s orbit when Earth is farthest from the Sun.  July Distance A Distance B  Distance B (the tilt) is so small that it really does not make us any closer to the sun.

3 Why do we have seasons? Seasons are caused by different amounts of sunlight reaching earth because of a combination of 1. The tilt of Earth and 2. It’s revolution around the sun

4 TILT  The tilt of earth effects the angle at which the sun’s rays strikes the surface.  When rays strike at high direct angles, they are more intense, concentrated, and warm.  When rays strike at low indirect angles, they are spread out, less concentrated, and cool.

5 TILT  The tilt causes different location to get different amounts of solar radiation…just like our flashlights.  Areas where the rays strike at high, direct angles get more intense radiation and are warmer.  Areas where the rays strike at low, indirect angles get less intense light and are cooler.

6 TILT If the tilt where the only factor, then every location on earth would have one season and never change. One location would always receive the most direct rays and would always be hot. (On this graphic the Southern Hemisphere). Another location would always receive less intense rays and would always be cool.

7 Revolution In addition to tilt, earth’s revolution is also a factor that causes seasons. Earth’s revolution causes the suns most direct rays to strike at different locations as earth orbits the sun. When Northern hemisphere is facing the sun: Most direct rays over Northern Hemisphere. Striking at Tropic of Cancer Summer Solstice (June 21 or 22) When Northern hemisphere is facing the sun: Most direct rays over Northern Hemisphere. Striking at Tropic of Cancer Summer Solstice (June 21 or 22) When Northern hemisphere is facing away from the sun: Most direct rays over Southern Hemisphere. Striking at Tropic of Capricorn Winter Solstice (Dec.21 or 22) When Northern hemisphere is facing away from the sun: Most direct rays over Southern Hemisphere. Striking at Tropic of Capricorn Winter Solstice (Dec.21 or 22) Neither Northern or Southern Hemisphere faces sun. Direct rays over equator. Autumnal Equinox (Sept.22 or 23) Neither Northern or Southern Hemisphere faces sun. Direct rays over equator. Vernal Equinox (March.22 or 23) Neither Northern or Southern Hemisphere faces sun. Direct rays over equator. Vernal Equinox (March.22 or 23)

8 Seasons

9 Why do we have seasons? Seasons are caused by different amounts of sunlight reaching earth because of a combination of 1. The tilt of Earth and 2. It’s revolution around the sun

10 Length of Daylight You probably noticed with seasons comes longer and shorter days. Now you can understand why this is so… The main reason for longer and shorter daylight is earth’s tilt

11 Length of Daylight – Summer Solstice When the Northern Hemisphere is tilted toward the sun = Summer Solstice. More Sunlight covering the northern hemisphere than darkness. LONGER DAYLIGHT! June 21 or 22 – Longest Day of the Year Light = MORE (15 hours) Dark = LESS (9 hours)

12 Length of Daylight – Winter Solstice When the Northern Hemisphere is tilted away from the sun = Winter Solstice. More darkness covering the northern hemisphere than sunlight. SHORTER DAYLIGHT! December 21 or 22 – Shortest Day of the Year Light = LESS (9 hours) Dark = MORE (15 hours)

13 Length of Daylight - Equinox When the Northern Hemisphere is not tilted away from or toward the sun = Equinox (Vernal and Autumnal). Equal amounts of daylight and darkness everywhere. EQUAL DAYLIGHT! September 22 or 23 / March 22 or 23 Light = 12 hours Dark = 12 hours

14 The Sun’s Path From our perspective here on earth, the sun “appears” to take a path across the sky as seen on the graphic.

15 The Sun’s Path Notice that from March to June, the sun angle travels high in the sky = warm, summer weather. It takes its longest path across the sky at this time, and thus, we have the longest amount of daylight (15 hours).

16 The Sun’s Path From June to September, the sun angle gets lower in the sky again. The lower angle means cooler weather and the start of fall. Notice how the path is shorter, and thus, the daylight hours start to get shorter.

17 The Sun’s Path From September to December, the sun angle reaches its lowest point. This means very little solar radiation and cold, winter weather. Notice that how the sun’s path is the shortest at this time, and thus the amount of daylight is also the shortest at only 9 hours.

18 The Sun’s Path From December to March, the sun angle begins to rise again, the days start to get warmer, and spring arrives. Spring is marked not only by warmer weather from the higher sun angle, but also longer days.

19 Sun’s Path Across Sky


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