WHAT is the winter solstice, and why bother to celebrate it, as so many people around the world will tomorrow? The word “solstice” derives from the Latin sol (meaning sun) and statum (stand still), and reflects what we see on the first days of summer and winter when, at dawn for two or three days, the sun seems to linger for several minutes in its passage across the sky, before beginning to double back. [emphasis mine]The Santa Fe New Mexican had something on Saturday about the sun and the moon and the earth being opposite each other. (It's gone to recycle limbo in the garage.)
Another said something about the earth adjusting its tilt.
And some have noted that the full moon and the eclipse are happening at the same time. Quelle surprise!
The New Mexican formulation seemed to be a clumsy translation into words of what the writer might have understood. Cohen simply doesn't understand, nor do those seeing the earth adjust its tilt or being amazed at the conjunction of full moon and eclipse.
So let me explain lunar eclipse and winter solstice.
A lunar eclipse happens when the moon enters the earth's shadow. So the sun, earth, and moon are lined up. Usually at full moon, the moon is above or below the earth's shadow, so not every full moon is an eclipse, but every lunar eclipse is at a full moon.
And here's how it will look at various times, earth's shadow indicated.
Diagrams from Our Universe and Sky and Telescope.
Now the solstice. Cohen has the derivation right. It's about the sun standing still. Sort of.
The earth is tilted in its orbit. That tilt remains in the same orientation relative to the solar system, which means that it points more or less toward the sun at different times. At the solstices, the tilt is toward or away from the sun. At the equinoxes, it is at right angles to the sun.
[From Boquete Weather.]
So what does that have to do with the sun standing still?
Well, the sun doesn't stand still. It keeps doing what it's been doing all year and before that. We know (I think) that the sun doesn't actually move around the earth to provide day and night, but rather that the earth's rotation makes it look that way. So if we start with the fall equinox (from the Latin for equal night, because the day and night are of equal duration), then as the earth moves toward the winter solstice, the sun rises a little later every day and sets earlier. If you watch the sunrise, you can seen the sun rising a bit further south every day. It also sets a bit further south. On the solstice, that changes. The sun then rises and sets a bit further north every day after the solstice, and the days get longer.
So on the winter solstice, the sun stands still in its journey south.
"[T]he sun seems to linger for several minutes in its passage across the sky, before beginning to double back." And just what had you ingested before you saw that, Richard Cohen?
Update: Props to The Guardian for getting it right!