Tuesday, December 12, 2006

Tilting Time

The sun is setting. Through gaps in frosted tree tops, I can see bands of pink colour lingering on the blue-gray clouds.

According to SunriseSunset.com, we are within a day or two of our earliest sunset of the year, more than ten minutes before the hour of 5 p.m. Their calendar lists sunrise and sunset times to the nearest minute, so I can't tell exactly which day marks the turning point.

By the time the winter solstice rolls around, our sunset will be moving later again. In those last few days before the solstice, the shortening of daylight will be only on the morning side, with sunrise still moving later, right through until early January.

Why?

From a New Scientist article, Early Days, I have a shaky idea of how our days shift through this dark time of the year. The U.S. Naval Observatory offers what sounds like a more systematic explanation in The Dark Days of Winter, but my understanding still feels a bit unsteady.

The impression that stays with me is this. Solar days pulse slightly over the course of a year, making the time from one noon to the next longer and shorter. Time as measured by the sun does not march exactly to the beat of atomic vibrations. We don't correct our clocks for this pulsation. Although those 24 hours on the dial suggest that we are keeping track of solar days, we are really approximating them, and clock time wobbles around solar time without quite matching it.

Twice in the last month I've seen an "atomic clock" offered for sale. It's really just an electric clock that automatically resets itself when it detects a radio signal from an atomic clock in Boulder, Colorado. You can get one at Lee Valley; you can also get a sundial. With the atomic clock, you can make detailed observations of sunrise and sunset times and then try to get your head around their movements. With the sundial, you can observe the solar day directly, and not worry about how many wobbles of an atom fit into it.

4 comments:

Madcap said...

It's not the little smidgets of time that I'm grappling after, it's the great swathes and hours of darkness that are feeling like more than I can bear. I need a clock to wake me from hibernation once we've got more than 6 hours of proper daylight again.

arcolaura said...

Hmmm. Maybe you could calculate sun angles and then curl up in a spot where the sun won't come over the sill until just the right day.

My mom got one of those lights that are supposed to help ease SAD. It's much smaller than the early ones, with an array of LEDs giving a brilliant blue-white light, and apparently very little heat, so I guess it's fairly efficient. She hasn't commented yet about whether it's working for her.

Deb said...

Tomorrow (the 15th), according to an Internet-generated sunrise/sunset table, the sun will set one minute later than it has for the last few days. That's reason for celebration, although I have a hard time waking up in the morning to do my new yoga/Pilates routine!

arcolaura said...

Deb - mornings are sluggish here too. Those morning self-care things seem to have dissolved down to just sleeping as late as possible.

I was getting a teensy bit of yoga in my belly-dance class - I quite like the downward-facing dog (but I don't have big dogs around to interrupt!). Now I need to make my own routine for the holidays, or else the 180 reps of ab-work at that first dance class in the new year are really going to hurt!