Earth’s Movement

Day And Night

• The earth takes 24 hours to do one full rotation (spin) on its axis. Do not confuse with revolution, which means movement around the sun.
• The side of the earth facing the sun has day, the opposite side has night.
• As Newfoundland rotates away from the sun it appears that the sun is setting in the west.  The reality is that the earth is spinning from west to east and we spin away from the sun.
• Similar effect in the morning. We spin around eastward to see the sun again.

Idealized Sketch

Cloud Cover And Temperature

• Nightly cloud cover helps keep heat inside the atmosphere.
• Reduces the range of temperature from day to night.
• Clouds reflect heat that has been absorbed during the day. Reflects it back to earth.
• No cloud cover means the heat escapes giving colder nights.

• Deserts have broad temperature range due to low cloud cover.
• Heat can escape during the night causing high daily temperature to turn into low nightly temperatures.

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The Seasons

• Two features of the earth-sun relationship create the seasons (outside the tropics).
• The tilt of the earth's axis.
• The revolution of the earth around the sun (remember the difference between rotation and revolution).

• In December, the north pole points away from the sun and receives fewer hours of sunlight hence giving it shorter days. 

Equinox And Solstice

Definitions

• Equinox: Times of equal light and darkness (12 hours each – occurs twice per year, September and March).
• Solstice: Times of maximum daylight and darkness ( occurs twice per year – winter solstice in December and summer solstice in June).

Length of the Day

• The earth does not sit perfectly vertical but is tilted on it’s axis.
• As it moves in it’s orbit around the sun, the angle of tilt with respect to where you are on earth changes.
• In June, because of the tilt on the earth's axis, the north pole points towards the sun.
• This means more hours of exposure to the sun giving longer days. 

• Different latitudes on earth receive different directness or intensity of light at different times.  When the sun hits more directly the latitude gets hotter temperatures (summer).
• The more direct the sunlight the more intense the heat.  The further you move outside the tropics the more extreme the seasons.  The length of day varies as you move from the equator.

• When light hits the earth towards the poles it is on a low angle which decreases the intensity of heat. 
• The same light/heat energy is spread over a greater area.
• Longer summer day light hours means there are more heating hours and fewer cooling hours.
• Earth’s surface will maintain it’s heat.

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Seasonal Temperature Changes

• The northern hemisphere will have more sunlight and thus greater heat as it moves into the path of more direct sunlight. Spring and Summer – March to September.
• The northern hemisphere will have less sunlight and therefore colder temperatures as it moves out of this path – Fall and Winter.
• The reverse is true for the southern hemisphere.

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