‘Tis the time of year for making merry, and also for changing seasons. That’s what we’re doing today, Sunday, Dec. 21, at 9:03 a.m., the moment of the winter solstice, the first day of winter, and also the moment we start gaining daylight once again.
You’ve no doubt noticed that the sun takes a very low arc across the southern sky this time of year, rising in the southeast and setting in the southwest, spending less than nine hours above the horizon. Today the sun reaches its lowest point in the southern sky. This low sun angle means that we’re not getting nearly the amount of solar power and radiation as we did in the summer.
From now through late June, though, the sun’s arc across the heavens will get higher and higher, and we’ll eventually get warmer. However, the coldest weather of the winter is yet to come. Blame it on the north polar regions. There’s been little or no sun up there for some time now, and super cold air has really built up. The cold has to go somewhere, and the general circulation of global winds causes that frigid air to spill our way in intervals until early March. I call it the polar hangover effect.
(Mike Lynch)
The sun’s daily path in the sky reflects the daily and annual motions of the Earth. When you were young, you learned that Earth’s rotation causes the sun to rise in the east and set in the west. The Earth’s orbit around the sun also affects how we see our home star in the sky, mainly because the Earth’s axis is tilted to its orbit around the sun by a 23.5-degree angle. Today on winter solstice day, the Earth’s northern hemisphere – where we live – is tilted at the maximum angle away from the sun’s most direct rays. The noontime sun is shining directly over the latitude line called the Tropic of Capricorn, which lies 23.5 degrees in latitude south of the Earth’s equator. Does that 23.5 degrees sound familiar? It should. In our skies, the sun’s noon-time angle will be as far south as it can be in our sky, just 21.5 degrees above the horizon.
Six months from now on June 21, the day of the summer solstice, we’ll be on the other side of Earth’s orbit around the sun and the northern hemisphere will be basking in the sun’s most direct rays. That will be reflected in our sky as the sun takes a long, high arc from the northeast to the northwest horizon. On the summer solstice, the noontime sun is at its farthest northern point in our sky. That puts it at a high 68.5 degrees above the southern horizon at noon. After the summer solstice, everything goes in reverse; the sun’s path in the sky gets lower and lower and the days get shorter and shorter.
Ancient and not-so-ancient cultures were keenly aware of the sun’s annual cycle in the sky, and many worshipped it. There was much sun worship going on in Northern Europe. Ancient observatories like Stonehenge in southern Great Britain and the cave-like Newgrange in Ireland are examples of this. It’s no accident that the early Catholic Church established Dec. 25 as Christmas Day. No one really knows the exact date of Christ’s birth, but one of the reasons the church chose Dec. 25 was to counter the great pagan celebrations around the winter solstice, when the sun was “reborn” and began its climb into the sky.
I want you to enjoy your holiday season, and also enjoy the sun’s increasing power!
Mike Lynch is an amateur astronomer and retired broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is the author of “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications and available at bookstores and adventurepublications.net. Mike is available for private star parties. You can contact him at mikewlynch@comcast.net.
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