On Monday at 12:30 p.m., at the Dupont South escalators, you can witness a phenomenon that occurs only twice a year. And, no, I don’t mean a group of tourists who all know to stand to the right. (That never happens.) According to the calculations of architect Steve Kunin, that’s precisely — give or take half an hour — when the sun will align with the escalator shaft, creating a perfect tunnel of light from the top to the bottom.

This marvel isn’t the sort of thing most riders appreciate, but Kunin is enlightened by his line of work: “We pay attention to sun angles a lot.”

So a year ago, when he was on his way from his office to a lunch appointment and was stopped in his tracks by the amazing rays, Kunin decided to do some calculations to figure out when it would happen again.

Using approximations from Google Earth and his escalator know-how (most are tilted at a 30-degree angle, he says), Kunin created a 3-D computer model. He then analyzed how the escalator shaft would line up with the sun and came up with dates on each end of the winter solstice: Nov. 23 and Jan. 14.

He’s decided to dub these days Metrohenge Dupont. It’s partly an homage to Manhattanhenge, which occurs the two days a year when the sunset is exactly in line with the New York City borough’s east-west streets. There’s also some Stonehenge-esque intrigue: When Kunin tried to use his iPhone compass to determine the direction of the Dupont South escalator shaft, he encountered a problem with the magnetic field.

Kunin doubts these light events factored in to the design of Dupont — or any other Metro stop — unlike the pyramids and some churches that have been built with sun orientation in mind. But the alignment still seems like a good excuse to have some kind of celebration, so he made a special trip out of the office in November to check if his calculations were accurate. And they were.

“I was tempted to turn to the people around me and say, ‘Do you know what’s happening?’ But they were from out of town and didn’t seem interested,” says Kunin, who thinks Washingtonians need to find something else of significance happening this time of year to heighten the experience. “It’s not the start of spring, and it’s not the harvest season. Maybe there’s some historical event it aligns with.”

Turns out, Kunin is right about that, too. Jan. 14 is a popular celebrity birthday (send cards to LL Cool J, Jason Bateman, Dave Grohl, Maureen Dowd, Steven Soderbergh, Shepard Smith, Taylor Branch, Faye Dunaway and Julian Bond). In medieval times, Christians celebrated Jan. 14 as the Feast of the Ass (not even kidding).

It’s also celebrated as New Year’s Day by anyone following the Julian calendar. So maybe we should pop open some champagne? Just don’t drink any of it on the Metro.

Steve Kunin shot this image of Metrohenge Dupont on Nov. 23.