Tuesday, December 23, 2014

Sunset, sunrise, solstice

This post is tardy. But hey, what's a few days when the dang blog's been on life support for two years? Trying to resurrect the thing and make it meaningful again. Or for once.

Bit of an attitude problem as I type this; combination of the flu, no sleep, nasty cold medicines, and a howling north wind have made me cranky.

Last night (December 20) a spectacular sunset presaged the arrival of overnight cloud cover. The southwestern sky was gorgeous; gauzy and ephemeral clouds were streaked with fiery colors that seemed to soak into the very molecules of the air, bringing the sea of gas alive. Tendrils of light and shadow danced across the landscape from the horizon to the very tip of my nose, playful and warm and shot through with wonder and joy. Over the next half-hour the colors faded, oh so slowly, making each moment a brand new and once in a lifetime gift. There aren’t enough words to describe the colors, let alone the feeling of the experience, the lightshow I so often take for granted, the place where Earth and air and light produce real and honest magic, seemingly just for me. Click on the images to enlarge.
Sunset, EJE ranch, December 20, 2014

And then it was gone. Behind me a photocell decided the time was right and Christmas lights came alive, warming the now chilly evening with pinpricks of color and a diffuse glow of cheer. Our little tricks of flowing electrons and hot filaments and glowing noble gases can’t begin to compete with nature’s light show, but that’s okay. Competition isn’t the point.
Christmas Lights, EJE Ranch, December 20, 2014

Finished with their lightshow duties, the clouds flowed in and covered the prairie with an insulating blanket of water vapor, holding the infrared energy of sun-warmed Earth close and tight where it could keep the air temperature relatively more warm than otherwise.

The science of this phenomenon is delightful. Water vapor is opaque to infrared light (which we think of as “heat” rather than light but which differs from visible light only in frequency), preventing the flight of photons which would otherwise zoom away towards outer space if not held in check. Kept close to the surface, infrared photons crash into molecules of air, imparting kinetic energy. We measure this motion as temperature: more motion equals warmer and less motion equals cooler.

This is the real greenhouse effect, and it couldn’t be more different from the politico-ideological version.

Around me in the dark, across the pastures of the ranch, the comparatively warmer air affected the formation of ice in stock tanks. On a clear winter’s eve, ice would form, thicken and harden quickly, but on the overcast longest night of the year, the ice formed only slowly.

The clouds hung around throughout the night. As dawn approached, a thin wash of light began to suffuse the landscape a scant few minutes before sunrise. The sun peeked over the horizon at 7:17 a.m. on this, the shortest day of the year, the winter solstice.

Sunrise (on the 21st) was far different than last night's (December 20) sunset. Same sun, same angle, same clouds, but the colors were muted and dull, tending more toward silver and gray. The light frequencies aren’t that different, a matter of a few angstroms, but visually the difference was pronounced. No less beautiful, but the light seemed cooler, maybe even standoffish. The morning felt dull and chill and far less uplifting than the previous evening. Was the light so very much different or was it just my perspective?
Dawn +90, EJE Ranch, December 21, 2014

Although the morning felt chill the temperature was just north of the freezing mark and there was little ice to chop as I made my rounds. The cattle were seemingly content; cows and calves, inhabiting different pastures miles apart, grazing on stem-cured grass.
Cows graze stem-cured grass

As I finished up my morning chores the sun managed to finally fight through the overcast and shafts of brilliant golden light illuminated the prairie, turning brooding browns and greys to uplifting gold in an instant. As the light changed so did my mood and perspective. The chill vanished and my heart filled with warm delight. There must be magic in those angstroms.
Calves graze stem-cured grass

At 4:03 p.m. the moment of solstice arrived. The sun was setting in the southwest as another sunset came on. Although I looked closely, I couldn’t tell that the moment had arrived, couldn’t see whether the sun actually halted in mid-sky or not.
See that? The sun just stopped! Winter Solstice, EJE Ranch, December 21, 2014

The notion of the sun halting and reversing course is the Earth-centric view, of course. Although the Sun seems to move southwards in the summer and fall and northwards in the winter and spring, that’s just our perspective from the surface of our planet. In reality, so far as our solar system is concerned, the sun is fixed in the center of the system and the planets – including the Earth – orbit around it.

The Earth's orbit alone doesn't account for the apparent movement of the sun. Were it as simple as that the sun would stay fixed in the sky over a single point. Half of the planet would experience perpetual day and the other half perpetual night. The moon is a good example; it orbits the Earth and rotates on its axis only once per revolution, keeping one side, the side familiar to us, always facing the Earth. The other side – the so-called dark side – never faces our planet, and only since the advent of space flight and rocket trips to the moon has man ever had a glimpse of the dark side.

But Earth, which is not tide-locked into a single rotation per orbit as the moon is, rotates much more frequently, making 365 and a quarter rotations for each orbit around the sun. Each rotation takes just under 24 hours. From these numbers, 365.25 and 24, we derive the length of our year, measured in days, and the length of our day, measured in hours.

This is all very well, but the fact that the Earth rotates once per day and orbits the sun every 365.25 days doesn’t explain the apparent north-to-south, south-to-north movement of the sun.

And now we get down to cases. Earth is tilted about 23.5 degrees in relation to the plane in which it orbits the sun, the plane of the ecliptic. This is the same plane occupied by the other seven planets in their orbits of the sun. If the Earth stood vertical in the Plane of the Ecliptic, with the north pole straight up and south pole straight down, the sun would never move north or south. It would rise each morning in precisely the same location on the eastern horizon and set each evening in precisely the same location on the western horizon. Each period of day and night would be the same from day to day, and those periods would be very close to 12 hours for most of the planet.
How it all works, more or less. From the interwebs.

Earth's axial tilt remains constant (at least in our very short temporal frame of reference) as the Earth orbits the sun. In the summer, the northern hemisphere is leaned over toward the sun, and the sun’s light shines more directly on the north half of the planet. In the winter, the northern hemisphere is leaned away from the sun, and the sun’s light shines less directly on the north half of the planet. If you live below the Equator, in Australia, say, the process is exactly reversed, and your summer begins in late December while your winter begins in late June.

All in all, three things have to work in concert to provide the seasons and the apparent solar movement we see. Earth has to orbit the sun. Earth has to rotate. And Earth has to be “leaned over” with an axial tilt.

There is wonder and magic in every single thing in the universe.

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