Michigan 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.
Axis • Axis – an imaginary line which the earth turns around • The earth is tilted at about 23.5 degrees.http://upload.wikimedia.org/wikipedia/commons/6/61/AxialTiltObliquity.png
Rotation• Rotation – turning around on an axis• It takes the earth about 24 hours to complete one rotation around it’s axis. This is also known as a day. http://upload.wikimedia.org/wikipedia/commons/3/30/Globespin.gif
Revolution• Revolution – one object traveling around another in a circular or elliptical pattern• It takes approximately 365 days for the earth to make one revolution around the sun. This is also known as a year.
What is a season?• A season is a subdivision of a year.• We have four seasons on earth: winter, spring, summer, and fall• During seasons, hours of daylight and weather may vary greatly depending on your location on Earth.
So What Causes Seasons?• There are two major causes for seasons on Earth. – 1 – the tilt of the earth on it’s axis – 2 – position of the earth in relation to the sun (revolution)
Winter• We are going to focus on the seasons in the Northern Hemisphere (that’s where we live).• During winter, the earth is titled away from the Sun.• This results in the Northern Hemisphere not getting strong, direct rays from the Sun. This is what causes winter.• A cool fact is we are actually closer to the Sun in the winter than in the summer.• The amount of night hours exceeds daylight.
Summer • During summer in the Northern Hemisphere, the earth is tilted towards the Sun. • This results in the Northern Hemisphere getting direct rays from the Sun. • The amount of daylight exceeds the amount of night hours.
Spring and Fall• In the spring and fall seasons, temperatures are generally mild• Daylight and nighttime hours are almost equal
Southern Hemisphere• We have already explored seasons in the Northern Hemisphere.• In the Southern Hemisphere, the seasons are opposite.
Exceptions• In tropical regions –those located around the equator do not received the four seasons.• Their “seasons” are wet and dry.• In polar regions, during their winter, they may only receive a few hours of daylight each day and in the summer, only a few hours of darkness.• This is because they are either tilted towards the Sun the most or they are tilted away from the Sun the farthest.
Video Clips• Seasons Aren’t Dictated By Closeness to the Su S• How Earth’s Tilt Causes Seasons
Quiz• What are the two factors which cause the seasons on Earth?• Are we closer to the Sun in the winter or summer?
Sources• http://www.dictionary.com• http://upload.wikimedia.org/wikipedia/commons/3/30/Globespin.gif - Animated Earth spinning on axis.• http://upload.wikimedia.org/wikipedia/commons/6/61/AxialTiltObliquity.png - Image of Earth on axis• http://en.wikipedia.org/wiki/File:Seasons1.svg – Image of Earth in Relation to the sun• http://www.khanacademy.org/science/cosmology-and-astronomy/v/seasons-aren-t-dictated- - Video Clip• http://www.khanacademy.org/science/cosmology-and-astronomy/v/how-earth-s-tilt-causes-s - How Earth’s Tilt Causes Seasons