Third midwinter

If you saw this morning’s sunrise, it was in a sense midwinter for you. It was the latest sunrise in the whole year, at any rate for a mid-US latitude of 40 degrees north, as we explain at perhaps laborious length on page 33 of Astronomical Calendar 2015.

We could call it the third of four midwinters. The first is the earliest sunset, around Dec. 8, when days seem shortest because they end soonest. The solstice of Dec. 21 is the second and most arithmetically solid midwinter, bringing the shortest day and lowest Sun. Then there’s this third midwinter, the day that begins latest for early risers. And the fourth and most tangible midwinter, the pit of cold, may come around the end of February! They say “The coldest hour is the hour before dawn,” and the coldest month may be the month before spring.

For my children at latitudes 38 and 36 the latest sunrise is yet to come, around Jan. 7. For me at latitude 51, it happened back on New Year’s Eve. I was probably out watching but forgot to be aware of this fact about it. I wasn’t out seeing it and sympathizing with you this morning because I won’t be riding again, or on clifftops to watch sunrises, till I know I’ve properly healed from my last fall off a cliff. In any case the difference between sunrise times is not a readily a noticeable phenomenon. Around such a date when something is reaching an extreme, it is changing most slowly, by only seconds.

This third midwinter may have been somewhat more real for cultures that were in the habit of watching for the Sun to rise, and for the stars to make their first “heliacal risings” before it; for instance, the priests of ancient Egypt. For them, at latitudes (between about 31 and 24) nearer to the equator, latest sunrise would have come some days later, about Jan. 11 or 12 (Gregorian) – further from the solstice. Still, one wonders whether they might have timed sunrises by means of sundials or water clocks and recognized the latest sunrise as the moment when the Sun began to return northward.

Really it would be feasible to discriminate sunrise times only on a flat horizon such as a sea or desert. Most sunrises are seen on elevated and irregular horizons.

An instant of sunrise some months ago – actually on 2013 April 30.

I want to take the risk of adding something that will happen near the equator of our planet tomorrow, Tuesday. Some very brave people born into a minority (a sexual one) in Uganda will be risking their lives by handing out a free publication.


5 thoughts on “Third midwinter”

  1. No longer confused, just agreeing to disagree. Still standing my ground that the seasons begin on the solstices and equinoxes, and if you’re party to one and I, a party to the other, fine! That’s twice as many parties. Whoopee!!! Happy winter, or what’s left of it.

  2. Midwinter seems to me a poetic construction (think of the Christmas Carol, “In the Bleak Midwinter”), and the charming idea that there might be four midwinters reinforces this feeling.

  3. Even more interesting would be to find ways to measure if winters are getting shorter because of climate change.

  4. I’m confused as to why this is being called mid-winter when, in fact, three of the four cases you describe seem more to describe the beginning of winter. Anywayz, Happy New Year!

    1. There’s a disagreement about whether to call the solstices and equinoxes the “middles” or “beginnings” of the four seasons. I belong to the party that calls them the “middles.” It’s simplest: they are the moments when the Sun is northernmost, on the equator, southernmost, and again on the equator. The other convention or habit, often seen in newspapers, is to call Dec. 21 the “beginning” of winter, March 20 the “beginning” of spring, and so on. This must be what Jack has in mind. The idea presumably arose because, though the Sun at Dec. 21 is lowest and most briefly in the sky, and will from then on get higher, the coldest times will come later, because of delay in the warming of the surface. This seems to me a fuzzy idea. If you’re going to define seasons by temperature, fine, but use actual weather, not arbitrary dates. You may think, for example, that climatic winter in your part of the world is roughly November to February. It’s highly unlikely to be exactly December 21 to March 20. That span of time is the span from astronomical (northern) midwinter to astronomical mid-spring.

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