Video From Barrow, Alaska, the day of Sunrise

We’re well south of Barrow, but when the sun rises there we know the Earth is really tilting more toward the sun. A video was taken by the FAA last Sunday, and to quote from the Weather Service Facebook page:

“Residents of Barrow, Alaska watched the sun climb above the horizon for the first time in 65 days, after it set on November 18, 2012. The sun skirted along the southern horizon for about 43 minutes today. Tomorrow it will remain above the horizon for 1 hour and 27 minutes. The amount of sunlight will rapidly increase in Barrow until May 10th, at which point the sun will remain above the horizon for 24 hours a day for nearly 3 months.”

I can’t seem to get the video to show on the page, but click here and you can see the Barrow sunrise.

Sunrise (and Sunset) in Fairbanks, Alaska

I had to share this video. For years I worked in an office with a south window just a block down the street from the museum from which this was taken, and I have seen the low arc of the sun over the Alaska Range. This video was on the Alaska Dispatch as a time-lapse of the Mayan Apocalypse (which just happened to be the Winter Solstice) with comments from the photographers.

The museum (and my old office) are on a ridge north of the Tanana Valley, with the main part of Fairbanks to the southeast, and part of the residential portion of College directly to the south. The bright patch below the Alaska Range on the horizon is the sun reflecting off the top of the ice fog; the discrete streamers are exhaust from chimneys.

Fairbanks Weather 9/26/11

It’s fall—and to prove it we’ll have only 11 hours and 52 minutes of daylight today. The sun rose at 7:45 this morning and it will set at 7:37 this evening – no more attending things that start at 7 pm, unless I can be sure of a ride back. At its highest the sun will be not quite 24° above the horizon, and days are now longer than those everywhere to the south of us..

Officially, we started fall last Friday at 1:05 in the morning, but it wasn’t until Sunday that we got down below 12 hours of daylight. Why? Because sunrise and sunset are defined according to when the top of the sun, not the middle, is just visible on the horizon. To be exact, you actually have to take into account also the fact that the atmosphere curves the path of the light rays slightly, so that the actual position of the sun is always a little lower in the sky than what our eyes tell us. This is only important when the sun is very near the horizon, of course, but at high latitudes, where the sun rises and sets at a very shallow angle, it can make several minutes difference in the time of sunrise and sunset. This also changes the apparent direction of sunset and sunrise – on the day of the equinox the sun actually rose 2° N of due east, and set 1° N of due west.

The weather has, sad to say, caught up with the season. We had a frost Saturday night, and only the hardiest plants are still going strong. I pulled the rest of the beets yesterday, and picked the few beans that were ready, as well as removing the hoses and laying them out to drain. I’m glad I brought in the potted plants last week. Next step? The potato bag.

The native deciduous trees have lost most of their leaves, with the exception of a few golden holdouts, and even exotics like my Amur maple are close to dropping their foliage. The world has changed form green to shades of tan. Even the evergreens are darkening. Good-bye, summer. See you next year.

Fairbanks Weather 9/12/11

Sunrise was at 7:04 this morning and sunset at 8:29 this evening, for a daylength of 13 hours 25 minutes. We’re losing 6 minutes 39 seconds a day. The sun at its highest is a little more than 29° above the horizon, and now dips more than 18° below the horizon — astronomical night. At the same time the full moon, which of course is opposite the sun in the sky, is getting higher in the sky — almost 25° tonight. The last quarter will be higher yet.

Amur maple in my yard. It has some anthocayanins, but as an exotic is slow to turn color.

I put the plastic covers over the beans and squash last night, and brought in the geraniums. The late-planted green beans are almost ready to pick, and as this is a new variety for me, I at least want to find out what they taste like! Turned out it wasn’t necessary, though, as the temperature at sunrise was 36F.

The trees are at that stage where some are green with just a few yellow leaves, some are about half turned, some are all gold, and some are already turning tan and losing their leaves. Yellow leaves sprinkle my lawn. There are even a few clumps of red-orange on the hillsides.

Clumps? Yes. Aspens, like birch, normally turn yellow in the fall, not orange. But a few mutant aspen do show a lot more red than usual in their foliage. Single trees would be hard to spot, but aspens spread by growing new shoots from their roots. This is decidedly problematic when you have a lawn bordered by aspens; trees are constantly poking themselves through the grass. But it also means that a stand of aspen is often actually a clone, each tree identical to its neighbors genetically. If one of the mutant trees with more red than usual in its fall coloring starts forming a spreading clone, the result is a red patch on the hillside.

The photo, looking ENE from a parking lot on the north side of Fairbanks, shows two such clones on Birch Hill. The more obvious is on the right side of the picture, just below the horizon. The other, smaller clone, is above and to the left of the Home Depot sign. More than likely, the uniform light green areas are other clones, ones that turn color late.

Sunrise

Sunrise

©Sue Ann Bowling

The scarlet sky repeats itself in the glass river below.
Wind rustles the grass on the banks–
A broom on a dirt floor might make such a sound.
High above birds circle, black flecks against the lightening sky.
Eagles, perhaps?  Kites?
Far off a radio babbles, mere noise against the wind.

An eddy moves toward shore, spinning a dismembered hand.
A torso follows, cleaver-hacked, trailing the coppery odor of blood.
Blue sky, sun risen now, the river
Still dyed scarlet with blood and anger.
The radio rises to a scream; cuts off.
Kites and eagles gather for a rare feast.

Another poem from 2007  Summer Arts Festival. I’ve forgotten the exact prompt, but I believe it involved specific words like glass, copper, radio. Somehow it came out as this image of conflict. Poems, for me, quite often form themselves into something totally different from anything I have in mind.

Why 12-Hour Days Already?

We broke 12 hours of daylight Friday, 2 days before the equinox. Why? And is this just due to my being close to 65 degrees North, or is it a more general anomaly?

There are two parts to this peculiarity. One is latitude combined with the finite diameter of the sun, which can be calculated. The other is the refraction of the atmosphere, which varies from day to day and can only be estimated.

Let’s take latitude first. Sunrise and sunset are defined as the time that the upper edge of the sun is just visible above a flat horizon. “Equal days and nights” (which is what equinox means) assumes the dividing line between day and night is the time when the center of the sun is on the horizon, assuming light moves in straight lines. If the sun rose vertically, as it does at the equator, it would rise at a rate of about 1 solar diameter a minute, and the calculated sunrise time based on the center of the sun would be only half a minute after the time the upper edge first showed.

At higher latitudes, however, the sun appears to rise at an angle and sunrise and sunset appear slower. At 65 degrees latitude the sun’s path at the equinox is 65 degrees from the vertical, and a little trigonometry stretches that half minute to about 1 minute 10 seconds, or twice that in day length. Latitude alone is still not enough to allow our days to be 12 hours 15 minutes long at the equinox. For that, the refraction of the atmosphere becomes important.

The apparent break in the spoon handle is due to refraction.

Everyone is familiar with refraction, though you may not know it by that name. The optical illusion of a broken spoon in water is caused by the fact that the speed of light in water is less than that in air. Yes, the speed of light in vacuum is constant, but in any other transparent medium it moves a little slower. When it crosses a boundary between two transparent media with different speeds of light, any light rays not moving at a right angle to the boundary are bent. Air is one of those transparent media, and while the speed of light in air is not a great deal slower than that in vacuum, there is enough of a difference that the bending affects what we can see.

The actual difference in speed depends on the density and moisture content of the air, which in turn depend on pressure, temperature and relative humidity. Air near the ground is almost always denser than that above it, and this is particularly true at sunrise. The change with height is gradual, and thus the light rays are not bent sharply, as in the water-air interface, but curved along the earth’s surface. Objects far away appear higher than they are, and this certainly applies to the sun at sunrise. The amount by which the sun appears higher in the sky than it really is will depend the atmospheric density and how it changes with height.

For practical purposes the time of sunrise is calculated assuming that the upper edge of the sun is visible when the center of the sun is 50 minutes of angle—almost a degree—below the horizon. This also means that the sun at the equinox will rise not quite due east, as it “rises” while it is still physically below the horizon and slightly north (in the northern hemisphere) of east. The difference, however, is slight.

Refraction is also responsible for the fact that the sun appears to flatten as it approaches the horizon when setting or just after rising. The part of the sun closest to the horizon is more strongly affected by atmospheric refraction than is the upper part of the sun, so the two appear pushed together and the sun appears flattened, rather than round. I’ve probably overused this in Tourist Trap.