T he sun will set at 4:25 p.m. in New Haven tomorrow. It’s the winter solstice, the shortest day of the year, though it doesn’t have the earliest sunset. That already occurred on December 8, at 4:22 and change.
This is just one of the curious quirks of the solstice. Many of us laypeople may be inclined to keep things simple: Earth is tilted on its axis; when the Northern Hemisphere is tilted away from the sun, we get winter; and the winter solstice happens when we’re tipped farthest from the sun.
But just because we’re tipped away from the sun doesn’t mean we’re at our farthest point from it. That’s because Earth’s orbit is elliptical, not circular, explains Hopkins School science teacher Ian Clark. “The seasons actually have absolutely nothing to do with our distance from the sun,” he says. “It’s all the tilt of the axis.”
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On that elliptical orbit, Earth’s farthest distance from the sun is called the “aphelion,” and due to shifts in our orbit, this point changes over time. This year, it fell on July 4, when we were a little over 94.5 million miles away. We’ll reach our next “perihelion,” or closest point to the sun, on January 4, at a mere 91.4 million miles away. Hence, at the moment, the hottest season coincides with our greatest distance from the sun, while the coldest season happens when we’re closest.
Here’s a burning question: Why, if we’re at our greatest tilt from the sun today, aren’t we experiencing the coldest depths of winter? Clark suggests we think about the inside of a car on a hot summer day. Metal parts such as the buckle of your seatbelt might be very hot, but a bottle of water might simply be warm to the touch. That’s because water has a high specific heat: “It takes a lot of energy before it changes temperature a little,” he explains. “It takes time for the oceans and the land surfaces to reach their maximum—or minimum—temperature. That doesn’t happen for about four weeks after the two solstices.”
As for the fact that sunset times don’t shift in perfect sync with the solstice—and that we’re already three minutes on our way back toward those glorious late sunsets of June and July—a “complicated combination of geometries” are at play, Clark notes, like “the tilt of the Earth and the plane of the orbit and the fact that we are a spinning sphere.”
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Further complicating matters, we’ve imposed human order on solar time. Take the concept of noon, for example. “Local noon” is the time when the sun is actually at its highest point in the sky over any particular location. But for the sake of living in an increasingly connected world, we now live in time zones. Thus, noon on your cell phone almost certainly isn’t actual noon. “Before we had fast travel and fast communications, if you rode your horse… for 50 miles, the town you arrived at would have a slightly different time,” Clark says. “You’d have to reset your pocket watch because they would set all of their clocks off of local noon.”
This winter’s latest sunrise, by the way, hasn’t happened yet. New Haven’s will occur a little before 7:18 a.m. on January 4. So, if you’re an early riser, don’t expect the sun to start peeking through your blinds to wake you just yet.
No matter when you rise, these days are short. Many of us travel to work and home again in the dark or half-light. Children walk home from school through the last long shadows of the day. Dinner is a sunless affair. Maybe breakfast, too.
On the bright side, by New Year’s Day, we’ll have gained eight minutes of afternoon sun, and by the end of January we’ll be bidding it goodnight at more respectable times, after 5 p.m. This annual spell of very long nights goes on long enough to sternly remind us what it feels like to be held away from the star that gives us life and, when the time comes, to appreciate its warmer nature.
Written by Kathy Leonard Czepiel. Image, taken at New Haven’s East Shore Park the day before a past solstice, photographed by Dan Mims. This updated story was originally published on December 21, 2017.
