By Carol Tannenhauser
Why do you think the Winter Solstice, which occurs this year in the northern hemisphere on Tuesday, December 21, at 10:59 a.m. EST, has the least amount of daylight of any day of the year — nine hours and 15 minutes to be exact?
“There was a famous study in which Harvard undergraduates were asked what they thought was the reason for the Winter Solstice,” said Dr. Jackie Faherty, an astrophysicist at the American Museum of Natural History. “Seventy-five percent of them thought it had to do with the distance of the Earth from the Sun.”
You mean, it doesn’t?
“Absolutely not,” said Dr. Faherty. “We’re actually closer to the sun at the time. It’s the tilt,” she added, graciously leaving off the “stupid.”
“Don’t worry,” she said. “It’s not like everybody knows this. I have to explain it even to the brilliant, because the distance seems intuitive; it feels like the right answer.”
But if it were, she asks, why would South Americans be basking in long hours of warm, beautiful sunlight now, celebrating their Summer Solstice?
“The tilt of the Earth on its axis by 23-and-a-half degrees is everything,” Dr. Faherty explained. “It means that sometimes you’re leaning a little bit more directly into the sunlight, and sometimes you’re leaning a little bit less directly into it. And for us in the northern hemisphere, we have reached the point where we’re leaning the furthest that we’re going to get from the direct sunlight. So it’s the day that’s the shortest; that’s how it translates.”
Another mistake, Dr. Faherty said, is to dread the shortened day. “It should be celebrated,” she said, “because it’s a transition day. It marks the start of winter — but also the days are going to get longer and the sun will get higher in the sky.” As The Old Farmer’s Almanac put it, “It only gets brighter from here.”
“Figuring out that the earth had a tilt was the beginning of the opening of our knowledge about the universe,” Dr. Faherty concluded.
If you would like to learn more about the Winter Solstice, here’s a link to an AMNH video called Reason for the Seasons.
The discussion of the Winter Solstice starts around minute 11.