"Earth Lighting Winter Solstice" by Przemyslaw "Blueshade" Idzkiewicz / CC BY-SA 2.0

Winter Solstice: The Science of the Shortest Day of 2018

Dec 21, 2018

By Laura Geggel

The winter solstice is in full stride today (Dec. 21), which boasts the fewest hours of daylight for 2018 in the Northern Hemisphere.

Although the solstice gets an entire day of recognition, it happens in an instant: at 15:23 p.m. EST (10:23 p.m. GMT), when the North Pole is at its farthest tilt of 23.5 degrees away from the sun. This position leaves the North Pole beyond the sun’s reach, and plunges it into total darkness, according to EarthSky.org.

In the Southern Hemisphere, the sun will shine directly overhead at Noon at exactly 23.5 degrees south of the equator, along the imaginary latitude line known as the Tropic of Capricorn, which runs through Australia, Chile, southern Brazil and northern South Africa. This is when when the sun appears to be at its southernmost point in the sky; as such, the Southern Hemisphere has its longest day of the year, and the Northern Hemisphere has its shortest day of the year, on the December solstice, according to EarthSky.

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