Classical Astronomy

The blog of the Classical Astronomy Update, a free email newsletter especially for Christian homeschool families about astronomy happenings in the night sky (though everyone is welcome!) Also, watch this space for progress reports about "Signs and Seasons," the author's upcoming homeschool astronomy curriculum!

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The Winter Solstice

5:39 PM, Saturday, December 20, 2008
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I thank Thee, Lord! The whiteness
Of winter on my heart
Shall keep some glint of brightness
Though sun and stars depart.

-- William James Linton (from The Old Farmer's Almanac, 1903)

During December, the Sun passes through the stars of Sagittarius the Teapot. This constellation is therefore not visible at this time, hidden behind the Sun's bright glare. The Sun is now in the southernmost portion of its annual path through the zodiac constellations, and thus rises and sets far to the south.

(from Signs & Seasons: Understanding the Elements of Classical Astronomy)

On about December 21 each year, the Sun reaches the southernmost extent of its annual cycle. This day is known as the winter solstice and is traditionally regarded as the official "first day of winter" for observers in the northern hemisphere.

On this day, the Sun is at its lowest point of the year in the noon sky as seen from the northern latitudes. The Sun never gets too high off the ground at noon as seen from the temperate zone. On this day you can measure the longest noon shadows of any day of the year.

After reaching its most southerly declination on the winter solstice, the Sun will appear to head north again, following its annual cycle through the seasons. In the coming months following December, keep your eye on the noon shadows, and notice how the they get shorter as Sun moves higher to the north in the noon sky, until reaching its northern maximum on the summer solstice in June.

On the winter solstice, since the Sun rises and sets very far to the south, it is not in the sky for very long. For this reason, the winter solstice is also "the shortest day of the year" since the length of daylight is shortest for people living north of the equator.

Here in Cleveland, the daylight on the shortest day lasts about 9 hours. Cleveland is near latitude 40 degrees North, along with many other large American cities, such as New York, Washington DC, Chicago, and San Francisco. So the length of daylight is about the same for these cities as well.

However, the length of winter daylight is even less for places further north. At the Arctic Circle, the Sun rises directly in the south at noon and immediately sets. In Alaska and Iceland, daytime is simply an extended twilight on either side of the noontime sunrise/sunset, and the Arctic nights of early winter are long and dark.

(from Signs & Seasons: Understanding the Elements of Classical Astronomy)

Meanwhile, December 21 is the summer solstice and thus the longest day of the year for people in the southern hemisphere. Folks in New Zealand, Australia, and South America are enjoying warm days and late sunsets we northerners shiver in the dark! But please don't envy them, they get their payback in June since their shortest day of the year is our longest!

The solstices and other aspects of the Sun's annual cycle are explained in detail in Chapter 5 of our Signs & Seasons astronomy curriculum. Remember, S&S isn't just for homeschool students! An increasing number of parents (especially the dads) are reporting that they are also learning a lot!