When it comes to the change of seasons, astronomically speaking, there is nothing new under the sun.
"This is one of the things humans have really understood through experience longer than just about anything else," said Grant Wilson, head of the Astronomy Department at the University of Massachusetts Amherst, standing in the center of a sunwheel built on campus around the year 2000.
It looks like a mini Stonehenge.
"It's probably, I guess about 30 yards across," Wilson said. "And we can see these big stones, they're taller than I am, for the most part."
Sunday, the sun rose and and set precisely at the south-eastern and south-western stones. The winter solstice happens in late December, right around the 21st or 22nd, Wilson explained.
"It's the time of year when the Earth's axis that it rotates around is tilted most strongly away from the sun. So in the Southern hemisphere, they're right now having the southern part of the earth kicked out towards the sun. They're getting very direct sunlight. And so they get to have summertime. Right now we get exactly the opposite, very glancing blows of sunlight. And in fact, our sun is only going to be about 23 degrees above the horizon at noon or around midday during the winter solstice [Sunday]," Grant said.
In the Northeast the highest the sun ever gets is during the summer solstice, Grant said, when it gets up to about 70 degrees above the horizon.
"During the winter solstice, it's much lower, and so instead of it shining down on us, it's really coming in from the side and really not as effectively warming the Earth. And that's why we're headed into winter now," he explained.
What's key about this day of the year, Wilson said is that we will have the shortest amount of sunlight [than] any other point in the year.
"That that varies just a little bit from year to year depending on when the actual solstice happens, and that happens because astronomical time as we keep it with the stars is not quite the same as solar time as we keep it with the sun," Wilson said, adding that — it gets complex to explain, and that's why the sunwheel is so interesting.
It literally brings it all right down onto the ground, carved out in stone, so that people can come out and experience.
"It is all just geometry. But it's complicated by the fact that we're [on Earth] also moving," Wilson said. " So we're spinning around our own axis. We're revolving around the sun. On the solstice will be the closest to the sun that we are going to be all year long. That's another surprising thing about it, because it's winter, you would think if you were closest, you'd be warmer. But no, it's just the opposite. We'll be closest to the sun, and we'll be moving faster in our orbit than at any other time during the year. So all of these things compound to make it a little more confusing than it otherwise would be," Wilson said.
On Sunday the winter solstice took place at 10:03 a.m., in the northeast. Easier to understand is that later that day, after the sun reached its southernmost position shortly after 6:30p.m., it began moving northward, and the days will, as expected, start getting longer.
