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The Reasons for the Seasons. Earth spins on axis (imaginary line through center of Earth from North to South Pole) Rotation is counter clockwise as seen from North Pole Earth spins on its axis like a top. Rotation. Polaris. Rotation - Axis. Earth tilt = 23.5 °
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Earth spins on axis (imaginary line through center of Earth from North to South Pole) Rotation is counter clockwise as seen from North Pole Earth spins on its axis like a top Rotation
Polaris Rotation - Axis • Earth tilt = 23.5° • Axis currently pointed at Polaris (the North Star)
Rotation • Earth rotates once every 24 hrs • The rotation causes day & night • Earth’s rotation causes celestial objects to appear to move from east to west in Northern Hemisphere
Revolution • Movement of one object around another • Earth revolves around our Sun • counterclockwise • Earth’s orbit is almost circular rather than oval shaped butis still referred to as an elliptical orbit • 365 ¼ days to revolve once around the Sun (~ a year)
Two Primary Reasons for the Seasons (on Earth) angle of Sun in the sky at a given time and latitude number of hours of daylight at a given time and latitude. Handout available at http://www.uwm.edu/~kahl/CoVis/Seasons/
Northern hemisphere tilts towards Sun = warmer (Summer) Seasons
Northern hemisphere tilts away from Sun = cooler (winter) Seasons
In the Spring and the Fall, the tilt of the Earth is such that the spread of sunlight shines on the Earth approximately equally Seasons
Southern hemisphere seasons are opposite Northern hemisphere seasons If its Winter here, then Australia is having _?_. Seasons
Solstices • Occur twice yearly when the Sun is directly over “Tropics” (23.5°N and 23.5°S Latitude) • Summer Solstice is the longest day of the year in the Northern Hemisphere (Sun directly over Tropic of Cancer-23.5°N-at noon) • Winter solstice = shortest day of the year for Northern Hemisphere (Sun directly over Tropic of Capricorn-23.5°S-at noon)
Equinox • equal night & day • Occurs twice each year • Half-way between solstices • noon sun directly over equator Sun will be at its highest point in our sky at noon but never directly overhead in Texas… why do you think this is true?
