Presentation on theme: "The Reason for the Seasons"— Presentation transcript:
1 The Reason for the Seasons EARTH’S TILTLength of Day – Angle of Rays
2 Why do we have seasons? NO Are the Seasons caused by the Earth being closer to or farther away from the sun?NOPerihelion is the point along Earth’s orbit when Earth is closest to the Sun.JanuaryCloser to the sun in January, and farther away in July.Aphelion is the point along Earth’s orbit when Earth is farthest from the Sun.JulyDistance BDistance B (the tilt) is so small that it really does not make us any closer to the sun.Distance A
3 Why do we have seasons?Seasons are caused by different amounts of sunlight reaching earth because of a combination ofThe tilt of Earth andIt’s revolution around the sun
4 TILTThe 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 TILTThe 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 TILTIf 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 RevolutionIn 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.Neither Northern or Southern Hemisphere faces sun.Direct rays over equator.Vernal Equinox (March.22 or 23)When Northern hemisphere is facing the sun:Most direct rays over Northern Hemisphere.Striking at Tropic of CancerSummer Solstice (June 21 or 22)When Northern hemisphere is facing away from the sun:Most direct rays over Southern Hemisphere.Striking at Tropic of CapricornWinter Solstice (Dec.21 or 22)Neither Northern or Southern Hemisphere faces sun.Direct rays over equator.Autumnal Equinox (Sept.22 or 23)
9 Why do we have seasons?Seasons are caused by different amounts of sunlight reaching earth because of a combination ofThe tilt of Earth andIt’s revolution around the sun
10 Length of DaylightYou 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 YearLight = 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 YearLight = 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 23Light = 12 hoursDark = 12 hours
14 The Sun’s PathFrom our perspective here on earth, the sun “appears” to take a path across the sky as seen on the graphic.
15 The Sun’s PathNotice 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 PathFrom 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 PathFrom 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 PathFrom 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.