December 21 marks the winter solstice, the official start of the first day of winter.
Technically, the solstice can happen any day between December 20 and December 23 because the calendars we use aren't the same length as a solar year. The sun is directly over the Tropic of Capricorn, with more sunlight seen in the Southern Hemisphere.
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It's often referred to as the shortest day of the year, and it is, sort of. The winter solstice has been honored as a time of divine births for a long time: in Persia, Mithras was said to have been born at this time and in ancient Egypt the date marked the birth of Horus. In an equinox the sun is right above the Earth's equator, making the day and the night the same length.
The term solstice literally means "sun stands still".
"Earth's axis is tilted 23.5 degrees relative to its orbit, and on December 21, Earth will be at the point in its orbit when the North Pole is tilted at its maximum away from the sun", Schneider told CBS News.
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If you weren't already familiar with the winter solstice, it's the day of the year where we have the least amount of daylight and longest stretch of night. Sunrise was at 8.03am GMT and sunset is at 3.53pm. This line is tilted 23.5° from Earth's orbital path around the Sun. The coldest days of the month often lag behind the winter solstice, coming in mid-January for cities like Chicago, Boston and even Miami.
At that time of the year, the Sun is moving at its slowest and so the solar day doesn't need to be quite as long because there's less ground to make up. From 2009 to 2012, she was an award-winning syndicated columnist for a number of daily newspapers from NY to Texas.
Of course, it's all opposite in the Southern Hemisphere, where December 21 marks the beginning of astronomical summer.
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In the Lower 48, the sun is up for more than 10 hours across Florida and southern Texas, while states across the northern tier get under nine hours of daylight. And that's why, for millennia, humans have celebrated the solstice-for the return of the sun that it marks.
So far we have only considered the tilt of the Earth.
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