The sun will rise this morning at 8:02, and set 11 hours 57 minutes later at 7:52 this evening. Since we’re now gaining 6 min 43 seconds a day, by tomorrow we’ll have more day than night.

But the equinox won’t be until 8:57 am Thursday the 20th! Why do we have equal day and night lengths before the equinox?

At the risk of sounding like a broken record, I’ll explain again. The equinox is defined by true sunrise and sunset, when the center of the sun would line up exactly with the horizon if light rays traveled in straight lines and your eyes were right on the ground. None of these assumptions are true.

In the first place, sunrise and sunset are defined by the first (and last) appearance of the top edge of the sun. At the equator, this differs by about a minute from the time as defined by the center of the sun. Where I live it is closer to 2 minutes.

The position of your eye doesn’t matter much normally, but I’ve seen the midnight sun (not normally visible at Fairbanks) from a small plane.

Finally, the atmosphere bends light, especially near sunrise and sunset. Exactly how much depends on the density structure of the atmosphere, which up here tends to produce a lot of bending. The numbers above are based on a standard atmosphere, so it is possible that the day length today is even longer than calculated.

At any rate, it is beginning to feel like spring. We had several thawing days last week, and I am sorry to say that some of the ice sculptures are beginning to melt, especially those with delicate parts. I went out again Friday to get some photos with the sun in a better position, and found a group of school buses unloading children! Luckily most were far more interested in the slides than the sculptures, so I was able to get some good shots. Some still looked pristine; some were slightly melted; some were partly collapsed. Here’s a pair of photos showing some of the damage wrought by the warm weather. Both photos are of “Guardian of the Deep” sculpted by Chris Foltz, Dean Murray, Jillian Howell and Amela Rombach, all of the USA. If you compare the two, you can see that Neptune has lost his trident, and the seahorse has lost a hoof and part of his mane.

Guardian of the Deep coldGuardian of the Deep 3:14:14Final comment: the warm weather seems to have ended. The coming week is forecast to be about normal: partly cloudy, no precipitation, highs in the 20’s and lows zero or a little below.

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