December 21 is a very important day for our planet and its relationship with the sun. December 21 is one of two solstices, days when the rays of the sun directly strike one of the two tropical latitude lines. December 21 marks the beginning of winter in the northern hemisphere and simultaneously heralds the beginning of summer in the southern hemisphere.

  A solstice occurs when the sun’s zenith is at its furthest point from the equator. During the December solstice it reaches its southernmost point and the Earth’s North Pole tilts away from the sun, at about 23.5 degrees.

The December solstice day has the shortest hours of daylight for those living north of the equator. Those living or travelling to the north of the Arctic Circle are able to see the “polar nights”, where the sun remains invisible throughout the night, while those living or travelling south of the Antarctic Circle will  see sun during this time of the year. The length of day temperature does not vary as much. On December 22, there are 24 hours of darkness north of the Arctic Circle (66.5° north of the equator) and 24 hours of sunlight south of the Antarctic Circle (66.5° south of the equator).

In the southern hemisphere, the December solstice is known as the longest day of the year. It is when the sun has reached its closet  point from the equator and marks the first day of summer.


  Axis is an imaginary line going right through the planet between the north and south poles. The axis is tilted somewhat off the plane of the earth’s revolution around the sun. The tilt of the axis is 23.5 degrees; thanks to this tilt, we enjoy the four seasons. For several months of the year, one half of the earth receives more direct rays of the sun than the other half.

  The equator is located at zero degrees latitude. The equator runs through Indonesia, Ecuador, northern Brazil, the Democratic Republic of the Congo, and Kenya, among other countries. It is 24,901.55 miles (40,075.16 kilometers) long. On the equator, the sun is directly overhead at noon on the two equinoxes – near March and September 21. The equator divides the planet into the Northern and Southern Hemispheres. On the equator, the length of day and night are equal every day of the year – day is always twelve hours long and night is always twelve hours long.

The Tropic of Cancer and the Tropic of Capricorn each lie at 23.5 degrees latitude. The Tropic of Cancer is located at 23.5° North of the equator and runs through Mexico, the Bahamas, Egypt, Saudi Arabia, India, and southern China. The Tropic of Capricorn lies at 23.5° South of the equator and runs through Australia, Chile, southern Brazil (Brazil is the only country that passes through both the equator and a tropic), and northern South Africa.

Longitude is the angular distance of any point on Earth measured east or west of a point on Earth’s surface.

When looking at a map, latitude lines run horizontally. Latitude lines are also known as parallels since they are parallel and are an equal distant from each other. Each degree of latitude is approximately 69 miles (111 km) apart;. Degrees latitude are numbered from 0° to 90° north and south. Zero degree is the equator. 90° north is the North Pole and 90° south is the South Pole.



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