In an earlier post, we noted that the plane of the Earth’s equator is tilted by 23.5 degrees from the plane of the Earth’s orbit around the Sun. This is the cause of the seasons. During autumn and winter in the Northern Hemisphere, the Earth’s North Pole is tilted away from the Sun, and we get more than 12 hours between sunset and the sunrise the next morning. The longest night occurs on December 21, when the North Pole is tilted the full 23.5 degrees away from the Sun.

We also can easily notice how the Sun’s noontime altitude is lower in autumn and winter than in spring and summer. At the latitude of Harrisonburg, the noontime Sun is highest on summer solstice day in late June: its altitude is about 75 degrees. At winter solstice, the Sun’s altitude is only about 28 degrees. This difference has a dramatic effect on shadows.

Imagine that you have a 6-foot fencepost standing vertical (as fenceposts should!). On every day of the year at local apparent noon, the post’s shadow points directly north. But the length of that shadow varies greatly during the year. On summer solstice day, the 6-foot post casts a puny shadow of about 19 inches. On winter solstice day, the noon shadow is more than 11 feet long. (On the equinox days, the noon shadow is 4 feet 9 inches long.)

Since on any given day the Sun reaches its highest altitude at noon, autumn and winter are the seasons of long shadows. In December and January, we have the longest shadows as well as the longest nights. At Harrisonburg’s latitude, the length of daylight (from sunrise to sunset) is less than 10 hours for all of December and most of January. Naturally this means that the length of night (including twilight) is more than 14 hours.

During the winter months, almost all of us go to bed after dark and some of us also arise before sunrise. Unfortunately, for many people, the long daytime shadows and long nights produce seasonal affective disorder (SAD). Spending some time in Florida or another southern location is often helpful – probably as much for the light as the warmth.

Although most of us spend most of the winter here on the Sunnyside campus, there are at least three compensations regarding stargazing. First, the winter constellations are the brightest of the year. Orion the Hunter has several bright stars (Betelgeuse and Rigel are the two brightest) and Canis Major (the Big Dog) has the very brightest star in the night sky: Sirius (the Dog Star). The winter constellations are shown below in an image from the ThoughtCo website ( [singlepic id="2220" float="none"] Second, because the wintertime atmosphere is drier (cold air can hold a smaller amount of water vapor than warm air) and contains much less pollen, on a clear night the sky is very dark. Third, simply because winter nights are longer, we can see more constellations during a winter night than we can during a summer night.

I’m an early riser, and during morning twilight on Thanksgiving I spotted a hot-air balloon from the south-facing kitchen window of our cottage in the Glen. I grabbed our camera and captured the image below. The photo was taken during one of the occasional brief moments when the flame was on. Since I don’t know the identity of the passengers or crew, maybe I should claim that I saw a UFO (unidentified floating object) over Sunnyside early on Thanksgiving morning!
[singlepic id="2221" float="none"]

--Bill Ingham