Astronomical Or Meteorological – Winter begins.

Shoveling Driveway
Driveway Snow Shoveling | Photo by Tim Chuey

I’ll bet most of you didn’t know that we actually have two definitions for the beginning of winter. According to the National Oceanic and Atmospheric Administration (NOAA) Astronomical Winter begins on or around December 21st and is determined by the position of Earth in relation to the Sun. It lasts until the Vernal Equinox on March 19, 2021. Meteorological Winter starts with the first day of December and lasts through January and February. For 2020 the season of winter officially begins with the Winter Solstice that occurs at 5:30 am PST on Monday December 21st. The National Weather Service defines the Winter Solstice as “the time at which the sun is farthest south in the northern hemisphere, on or around December 21.”The term is derived from a latin word, solstitium, meaning the sun (sol) and to stop (stitium).

Summer Solstice Diagram | graphics Bjarne Slewertsen / Danish Meteorological Institute
Summer Solstice Diagram | graphics Bjarne Slewertsen / Image by Danish Meteorological Institute

Here is a little refresher course on exactly what that means. We know that the earth revolves around the sun in an elliptical orbit around the sun. Two things determine the seasons of the year: the position of the sun in it’s orbit around the sun and the angle at which the sun’s rays strike the earth. The sun’s rays would be spread evenly over the earth if it weren’t for the fact that the earth is tilted 23.5 degrees from the plane of the ecliptic. That angle allows the sun’s rays to be concentrated in the northern hemisphere in the summer and in the southern hemisphere in the winter.  The Summer Solstice is when the concentrated solar rays have moved to their farthest point to the north producing the longest day of the year. As the summer progresses those rays migrate southward reaching the southernmost concentration on the Winter Solstice (December 21/22) which is the shortest day of the year.

Winter Solstice 2015 at Stonehenge – Overcast With Sun Peeking Out | Photo by

In between the Summer Solstice and the Winter Solstice are the Vernal or Spring Equinox and the Autumnal or Autumn Equinox. The equinox is defined by the National Weather Service as “the time when the sun crosses the earth’s equator, making night and day of approximately  equal length over all the earth and occurring about March 21 (the spring or vernal equinox) and September 22 (autumnal equinox).

Summer Solstice at Stonehenge | Image
Summer Solstice at Stonehenge | Image by

The arranged stones at Stonehenge in England have long been thought to have been built to honor the solstice. In an interview for an article in the Register (England) by Brid-Aine Parnelli it was explained that archeological teams from universities of Sheffield, Manchester, Southampton, Bournemouth, and University College London have been investigating Stonehenge for ten years. They feel the monument was built as a symbol of a complex farm-subsidy agreement. A statement by the scientists states that they think the spot already had significance to the people there and building the monument made it even more important. “The solstice-aligned avenue sits on a series of natural landforms that, by chance, form an axis between the directions of midsummer sunrise and midwinter sunset” according to the scientists. Professor Mike Parker Pearson from Sheffield University, interviewed in the article, said “This might explain why there are eight monuments in the Stonehenge area with solistitial  alignments, a number unmatched  anywhere else. Perhaps they saw this place as the centre of the world.”

Let me know what you would like me to talk about or explain. You can comment below or email me at: [email protected].

Tim Chuey is a Member of the American Meteorological Society and the National Weather Association and has been Awarded Seals of Approval for television weathercasting from both organizations.

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