The Feast of Crepusculus Winter-Rise

Okay, one more post about this solstice business, and then we’ll put it to bed for another six months or so.

January 3rd was the day, at my latitude, with the latest sunrise. Having safely passed that date, we are now well and truly growing the day at both ends. Despite cold days ahead, we can nevertheless look forward to rapidly expanding sunlight hours. That counts for a lot in my book. Anyway, as you can quickly deduce, there are four crepuscular extremes during the year: earliest and latest sunrise, and earliest and latest sunset. If we are to recognize the special nature of any of these days, we should be prepared to recognize all of them. With that in mind, I dub them Crepusculus Winter-Set, Crepusculus Winter-Rise, Crepusculus Summer-Rise, Crepusculus Summer-Set. Bit of a mouthful, I know, but it’s all in the name of thoroughness.

As part of pondering sunrises late and early, I asked myself this question: who shares the instant of that latest sunrise with me? It’s not hard to work it out on a map, but doing the calculations was fun. Here it is on a globe view.

And here we are zoomed in to the east coast of the U.S. As you can see, dawn’s rose-red fingers tickle almost the entire eastern seaboard at the same instant. I share that moment of daybreak with people from the western tip of Cuba to the north shore of Iceland.

If you’re curious about how I created the plot, I talk about it more in a MATLAB-related post over here: Crepuscular Isochrons: Sunrise Here and There.