The Sun’s Striptease
December 22, which is 4 days from now, is Winter Solstice. For those of us living north of the equator, it’ll be the shortest day of the year. For those of us living along the Arctic Circle, the sun will not rise above the horizon. On December 22, sunrise here will be at 11:37 am, and sunset will be at 12:25 pm, making a “day” of 48 minutes. In Boston on the same day, there’ll be 9 hours between sunrise and sunset.
So you ask, I thought sun doesn’t come up north of the Arctic Circle? It’s really a matter of definitions. Sunrise is defined by the lip of the sun peeking above the horizon, but the center of the sun could still be below the horizon. In fact, it’s 0.1 degree below the horizon now at its highest. But in truth, I haven’t seen the sun for a couple of weeks now because of the mountain range south of us on mainland.
In the morning, I walk with the children to school in complete darkness. At around 9:30 am, the sky starts to light up. How bright it becomes is highly dependent on cloud coverage. Some days when it’s very cloudy, it feels like day light never really came. But one thing that’s important to know about the North is that going from dark to light is very, very gradual. At high noon, it really looks like sunset. So in effect the entire day, if you could even call it day, is a 5 hour-long sunrise or sunset. This is why we’re treated with such spectacular skies. Further south, sunrise and sunset could be just as spectacular, but they happen so fast that the spectacular moments are fleeting. Unless your eye are peeled looking at the sky, you’d miss it. Here, just look out the window any time during those 5 hours.
I tried to figure out a good way to explain this scientifically, and I found these graphics online. If you spent time in the tropics, you’ll recall that sunrise and sunset happen very fast, and at noon the sun is directly overhead. Here, it takes a lot more time for the sun to rise or fall a few degrees relative to the horizon, and the sun always come at a sharp angle, even in the summer. Of course, in the summer, the entire path of the sun shift up, so there is more daylight. Now, the sun’s path is mostly below the horizon.
Another way to explain it is, the sun makes a path relative to the horizon over a 24 hour period, and the path is a sine wave. The horizon, or the x-axis, moves up and down based on the season, and the height of the wave is determined by your latitude. So you have the two variables that determine the sun’s path clearly visible:
No matter how you look at it, daylight is a good thing. I’m looking forward to the Spring. Meanwhile, since there’s nothing I can do about it, I’ll just continue to snap away at the sky.