I enjoy the yearly drama of the shortening days during December that are followed, just before Christmas, invisibly, by the knowledge of new light. It is the grand rebirth, the celestial reminder that darkest events in any sphere of life can give rise to brightening ones. This year I wanted details, so I printed out the times of sunrises and sunsets along with each day’s length, time of solar noon, and earth’s distance to the sun.
In the information were three surprises.
First, I have always assumed, as I’ll bet most people have, that what is happening as the days grow shorter is that sunrise and sunset steadily close in on daylight from both sides, as if the day were being squeezed equally at both ends by the night. And I thought that on December 21, the process reverses and daylight expands as the sun rises earlier and, by an equal amount, sets later.
Not so. As I looked down the printed columns of sunrise and sunset times, the two events seemed quite disconnected from each other. From one day to the next over several weeks, the change (from less than a minute up to two minutes) in the time of sunrise did not match up at all with the amount of change in the sunset time for the same day. So much for my notion that sunrise and sunset “squeezed” the day at the same pace. But even more surprising is the fact that they did not even change in the expected directions. They don’t jointly close in and then abruptly and simultaneously do an about-face on the 21st as I had thought. Sunrise keeps getting later and later even after the 21st all the way through the first week of January. Sunset, contrarily, reverses direction way earlier than the 21st, back on December 12. So what you get is both sunrise and sunset taking place later and later for a month, from roughly the first week of December through early January. The only reason that the length of daylight shortens and then lengthens during that period is that the two latenesses increase at differing speeds. At first it is the sunrise that gets later faster; after the 21st, it is the sunset.
The second surprise: I have always thought that noon was the time when the sun is at its highest point in the sky no matter what the season, even in winter when that high point looks only about half way up from the horizon. Wrong again. Solar noon, the sun’s highest point, falls a few minutes before noon through December, is at noon exactly on December 31, and then falls into the afternoon through January and February, when it reverses again. So much for “High Noon.” Not a big disillusionment, but a small shock to discover that what had seemed practically the definition of noon is only an approximation.
Finally, I knew that winter is cold because the earth’s axis in those months leans away from the sun, the sun’s rays and their heat are spread out over a wider area in the north than in summer, and the hours of light are fewer. I might have also bet (if I was forgetting the southern hemisphere’s summer for a moment) that the earth, if its distance from the sun changed at all during the year, is further from the sun when it is cold. More distance, less heat, right? But in fact on or about each January 3, the earth and sun are at their closest for the entire year. Not close enough to cancel out the cold, but enough to confound superficial common sense.
So it turns out, not surprisingly, that the daily interactions between earth and sun are more complex and contradictory than I had thought. What had seemed straightforward now seems at once more powerful and more delicate. Knowledge does that—you see more of the moving parts exposed for what they are. The billions of years of earth’s climate are full of surprises. But this December, the three surprises—like three solar Wise Men—dispelled some childish myths. Now, the duet of earth and sun seems vaster, and my time and place within it briefer and smaller.