The Homely Truth About the Shortest Day

We passed the shortest day of the year last week. It’s the annual drama of encroaching darkness turning to growing light, the grand rebirth, the celestial, uplifting reminder that in any sphere of life, the gloom gives way to brightness.

I’ve always imagined the event as accompanied by an elegant symmetry. I thought that the darkness closed in evenly from both sides, that the sun rose a little later each morning and set a little earlier until the shortest day on December 21st, when the process neatly reversed at both ends of the day. The sequence, I thought, between early December and early January had the shape of a tall hourglass. The left “sunrise” side sloped in to the right during most of December and the right “sunset” side sloped left, each changing by a minute or two each day. On December 21st, they met at the narrow waist and reversed direction.

scienceblogs.com

scienceblogs.com

Well, it doesn’t work that way. Changes in sunrise and sunset times aren’t in synch. The sun doesn’t neatly rise later each morning until the 21st and then reverse course. It keeps rising later and later well beyond the 21st, past Christmas and into the first week of January. Imagine the left side of the hourglass sloping down and right until it’s well below the waist.

The timing of sunsets changes in the opposite way. Sunsets change direction, from happening earlier to happening later, about a week before the shortest day. Imagine the right side of the hour glass sloping inward not all the way down to the waist but only part way. Such an hourglass would have a weird, uneven tube descending from the upper left to lower right. It isn’t until early January that both sides would be moving apart from each other again.

The shortest day is the shortest only because the speed of the changes in the times of rising and setting vary from day to day. In early December, the sun rises later by a sizable couple of minutes every day, while sunset drags on at almost the same time, so the length of daylight shrinks until the 21st. After that, the changes in sunrise slow way down while it is sunset’s turn to pick up the pace, getting rapidly later (by about 7 minutes between the 21st and New Year’s Eve in New York) and lengthening the day.

So the shortest day grows out of a ragged process, not the aligned and symmetrical one we thought we were seeing. The universe spins in ways that we don’t or can’t grasp in detail, but we pull the meanings that we need from our approximations anyway.

 

Summertime Blues

IMG_20150720_090706_367Mid July, and summer begins to turn hotter and drier. The growth of most plants is slowing and their leaves will soon turn a little duller. But it’s the start of the season for the thin stalks of bright, light blue flowers that grow close along the roads and in sun-hardened patches of earth in the angles of intersections. From a moving car, chicory is a tiny galaxy of sky blue dots and wheels pointed in various directions as they hug the road.

Chicory has been pushing its way into civilization for a long time. Its goes back 40 million years, when it differentiated from the daisies and marigolds in its family. Its medicinal uses date back to Egypt and Rome. Today it is still an effective toxin against parasites in animals. Its roasted root substitutes for and is added to coffee in Europe and the U.S. Its dandelion-like leaves make good salad; cultivated varieties of chicory include endive and radicchio.

Each flower blooms only for a day or two. Each plant lives for two years, flowering only during its second summer, after which the plant dies at first frost. Forty million years of fleeting life.

It’s the light blue flowers and their affinity for roadsides and compacted dirt that catch my attention. Chicory is apparently drawn to the warmth of the pavement. The ingenuity of life.

chicory Asteraceae (wikipedia.com)

“Asteracea poster 3” by Alvesgaspar, Tony Wills (10) – Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons –

Three December-21st Surprises (Not About the Non-End of the World)

Three December-21st Surprises (Not About the Non-End of the World)

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.