What Causes Seasons on What Causes Seasons on Earth?Earth?

By Nick SouthernBy Nick Southern

Michigan StandardsMichigan Standards

•E.ES.M.6 Seasons- Seasons result from annual variations in the intensity of sunlight and length of day due to the tilt of the axis of the Earth relative to the plane of its yearly orbit around the sun.

Key VocabularyKey Vocabulary

• RotationRotation

• RevolutionRevolution

• AxisAxis

AxisAxis

• Axis – an Axis – an imaginary imaginary line which line which the earth the earth turns turns aroundaround

• The earth The earth is tilted at is tilted at about 23.5 about 23.5 degrees.degrees.

http://upload.wikimedia.org/wikipedia/commons/6/61/AxialTiltObliquity.png

RotationRotation

• Rotation – turning Rotation – turning around on an axisaround on an axis

• It takes the earth It takes the earth about 24 hours to about 24 hours to complete one complete one rotation around it’s rotation around it’s axis. This is also axis. This is also known as a day.known as a day.

http://upload.wikimedia.org/wikipedia/commons/3/30/Globespin.gif

RevolutionRevolution

• Revolution – one Revolution – one object traveling object traveling around another in a around another in a circular or elliptical circular or elliptical patternpattern

• It takes approximately It takes approximately 365 days for the earth 365 days for the earth to make one to make one revolution around the revolution around the sun. This is also sun. This is also known as a year.known as a year.

What is a season?What is a season?

• A season is a subdivision of a year.A season is a subdivision of a year.

• We have four seasons on earth: We have four seasons on earth: winter, spring, summer, and fallwinter, spring, summer, and fall

• During seasons, hours of daylight During seasons, hours of daylight and weather may vary greatly and weather may vary greatly depending on your location on Earth.depending on your location on Earth.

So What Causes Seasons?So What Causes Seasons?

• There are two major causes for There are two major causes for seasons on Earth.seasons on Earth.– 1 – the tilt of the earth on it’s axis1 – the tilt of the earth on it’s axis– 2 – position of the earth in relation to 2 – position of the earth in relation to

the sun (revolution)the sun (revolution)

WinterWinter

• We are going to focus on We are going to focus on the seasons in the Northern the seasons in the Northern Hemisphere (that’s where Hemisphere (that’s where we live).we live).

• During winter, the earth is During winter, the earth is titled away from the Sun.titled away from the Sun.

• This results in the Northern This results in the Northern Hemisphere not getting Hemisphere not getting strong, direct rays from the strong, direct rays from the Sun. This is what causes Sun. This is what causes winter.winter.

• A cool fact is we are actually A cool fact is we are actually closer to the Sun in the closer to the Sun in the winter than in the summer.winter than in the summer.

• The amount of night hours The amount of night hours exceeds daylight.exceeds daylight.

SummerSummer

• During summer in the During summer in the Northern Hemisphere, Northern Hemisphere, the earth is tilted the earth is tilted towards the Sun.towards the Sun.

• This results in the This results in the Northern Hemisphere Northern Hemisphere getting direct rays getting direct rays from the Sun.from the Sun.

• The amount of The amount of daylight exceeds the daylight exceeds the amount of night hours.amount of night hours.

Spring and FallSpring and Fall

• In the spring and In the spring and fall seasons, fall seasons, temperatures are temperatures are generally mildgenerally mild

• Daylight and Daylight and nighttime hours nighttime hours are almost equalare almost equal

Southern HemisphereSouthern Hemisphere

• We have already explored seasons in We have already explored seasons in the Northern Hemisphere.the Northern Hemisphere.

• In the Southern Hemisphere, the In the Southern Hemisphere, the seasons are opposite.seasons are opposite.

ExceptionsExceptions

• In tropical regions –those located around In tropical regions –those located around the equator do not received the four the equator do not received the four seasons. seasons.

• Their “seasons” are wet and dry.Their “seasons” are wet and dry.• In polar regions, during their winter, they In polar regions, during their winter, they

may only receive a few hours of daylight may only receive a few hours of daylight each day and in the summer, only a few each day and in the summer, only a few hours of darkness.hours of darkness.

• This is because they are either tilted This is because they are either tilted towards the Sun the most or they are towards the Sun the most or they are tilted away from the Sun the farthest.tilted away from the Sun the farthest.

SeasonsSeasons

http://en.wikipedia.org/wiki/File:Seasons1.svg

Video ClipsVideo Clips

• Seasons Aren’t Dictated By Seasons Aren’t Dictated By Closeness to the SunCloseness to the Sun

• How Earth’s Tilt Causes SeasonsHow Earth’s Tilt Causes Seasons

QuizQuiz

• What are the two factors which cause What are the two factors which cause the seasons on Earth?the seasons on Earth?

• Are we closer to the Sun in the winter Are we closer to the Sun in the winter or summer?or summer?

SourcesSources

• http://www.dictionary.comhttp://www.dictionary.com

• http://upload.wikimedia.org/wikipedia/commons/3/30/Globespin.gifhttp://upload.wikimedia.org/wikipedia/commons/3/30/Globespin.gif - - Animated Earth spinning on axis.Animated Earth spinning on axis.

• http://upload.wikimedia.org/wikipedia/commons/6/61/AxialTiltObliquity.pnghttp://upload.wikimedia.org/wikipedia/commons/6/61/AxialTiltObliquity.png - Image of Earth on axis- Image of Earth on axis

• http://en.wikipedia.org/wiki/File:Seasons1.svghttp://en.wikipedia.org/wiki/File:Seasons1.svg – Image of Earth in Relation – Image of Earth in Relation to the sunto the sun

• http://www.khanacademy.org/science/cosmology-and-astronomy/v/http://www.khanacademy.org/science/cosmology-and-astronomy/v/seasons-aren-t-dictated-by-closeness-to-sun - Video Clipseasons-aren-t-dictated-by-closeness-to-sun - Video Clip

• http://www.khanacademy.org/science/cosmology-and-astronomy/v/how-http://www.khanacademy.org/science/cosmology-and-astronomy/v/how-earth-s-tilt-causes-seasons - How Earth’s Tilt Causes Seasonsearth-s-tilt-causes-seasons - How Earth’s Tilt Causes Seasons