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o The earth rotates about an imaginary line that passes through the North and South Poles of the planet.  This line is called the axis of rotation. 

o It is for this reason, that it seems that the sun:• Rises in the East• Is south at noon• Sets in the West

o This axis is tiltedo The rotation occurs from west to east over a 24-hour periodo

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o This rotation causes the cycle of day and night

o Since Earth is round and opaque, the sun can only illuminate one side at a time

o This is why when it is daytime in America, it is night in Australia

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o The Earth also turns around the sun in a path called an ORBIT at a speed of 29.75km/s

o It takes 365.25 days for one complete revolution (a solar year)

o Every 4 years the extra day is added to the calendar as February 29, this type of year is called a LEAP YEAR.

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o Because the Earth’s axis is tilted, our planet is in different positions during the year, giving us 4 different seasons

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o The solstices mark the points at which the poles are tilted at their maximum toward or away from the sun.

o The seasons are marked by solstices and equinoxes — astronomical terms that relate to Earth’s tilt.

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o Summer solstice o shortest night of the yearo sun is farthest northo first day of summeroJune 21 in Northern hemisphere

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o Winter solstice o longest night of the yearo Sun is farthest southo first day of wintero December 21 in Northern hemisphere

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o The equinoxes occur when the Earth is between solstices, it is spring and fall o Day and night have almost same duration all over the planeto Equinoxes occur on March 21 and September 23 in the Northern Hemisphere

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o At the equator, the sunlight hits the Earth’s surface at a 90˚ angle, which results in a more concentrated amount of sun in a given area.

o At the poles, the same amount of sun is shining but not at a 90˚ angle.

oThe rays therefore get spread out over a larger area, making the sun less strong over any given area.

CreditsCredits

Jessica Jessica Montreal, QCMontreal, QC