Through the Terminator

The first and last blasts of light and heat piercing our sky have inspired and awed human beings since before recorded history.  As a physics major that specialized in light and optics, I’ve always been fascinated by the elaborate interaction between our sun and atmosphere that are normally taken for granted.

First off, there’s the miracle of the sunlight itself.  The heart of the sun produces energy through the process of fusing hydrogen atoms together.  This energy is released in the form of photons of varying energy levels.  We experience these different energy levels as red through violet visible light along with the infrared heating our planet and ultraviolet giving us tans and sunburns.  But before these photons reach us, they take about a 50,000 year journey to reach the edge of the sun and then a little over an 8 minute trip through space to reach our planet

Some interesting things begin to happen as these varying photons hit our planet at the speed of light.  Lucky for us, many of the highest energy particles start getting absorbed in the higher layers of the atmosphere.  The next higher energy photons make it a little lower but start to get absorbed and radiated out in random directions by the particles in the lower atmosphere.  These particles get scattered throughout the atmosphere above us and eventually make their way to the ground and our eye registers it as the blue light of the sky.  At 70,000 feet, much of this process is happening below, leading to the black sky you see in these pictures and some additional blue hue to the planet below.

During the day, most of the rest of the blue light and lower energy photons reach the surface.  Every single thing we see during the day, unless it’s coming from an artificial light source, is sunlight.  The sky, that green tree, the person driving and talking on their phone, even the grey clouds on a gloomy day, are all perceived because sunlight is either being scattered or reflected into your eye after it’s remarkable journey.

As the Earth’s rotation moves you away from the sun, there is suddenly much more atmosphere to pluck away some more of the less energetic or lower wavelength photons.  The rest of the blue and little bit of green and yellow is the first to go leaving us with primarily orange and red light to bathe us and our surrounding clouds with.  With a little more filtering, that orange gets plucked out as well leaving a deep red.  Being close to 70,000 feet, as I am in the photo above, there’s not all that pesky atmosphere to strip the light away from me; while close to the ground, the clouds gets the full sunset treatment, reflecting its red-orange brilliance up to my camera.

When the sun sets, there’s an amazing display that happens every single day over your head.  Due to the pesky atmosphere and limited vantage point, we miss out on seeing the majesty of the terminator.  This is the literal dividing line between day and night.  If there was ever a doubt about the shape of the Earth, seeing the sun fall and the shadow rise during a sunset would forever remove all doubt. 

It is still one of my favorite sights while flying the U-2.  It was almost like you could literally see the lid being closed on the daytime, and night taking over.  Even I’m not completely sure about why this is so distinct from 70,000 feet.  Even more than 35,000 feet.  And I’m not sure what makes one so much more distinct that some others from altitude.  This one, taken on my next to last flight, still sticks in my mind for its distinct line and colors

As the lid is finally closed, the bright area where the sun was seems to stay much longer than it should.  Not visible from the ground, this light is still being refracted around the globe by the upper atmosphere.  A period of upper atmosphere twilight remains for well over an hour after the last sight of the sun.  It is there even after the stars have come out to play with their interstellar illumination.

Few humans on our planet really know the dim lights that shine over our world every single night.  Our modern world has made it impractical and unnecessary to keep a connection with the perennially changing light show going on directly over them every single night.  From a U-2 at night, I can see an unobstructed view of the heavens.  As a space enthusiast and photographer, I had always wanted to capture what I saw.  Just as the magic of the sunlight during the day showed the beauty of the world below, I hoped to bring an awareness of the majesty of the unfathomable expanse above through the lens of my camera.

On this particular moonless night, the stars were especially vivid.  Taking shots of stars in an aluminum can moving at 500 mph takes patience and a lot of really horrible pictures to sift through.  While these pictures have more noise and movement than you will see from any ground tripod mounted camera, they succeed in the very simple task I set out to do which was bring a piece of the heavens down to Earth.

How many thousands of times have we obliviously made the daily journey away from the sun and into the darkness of night without even a thought to the spectacular show going on around us.  Think of each photon, that has made such an incredible journey to reach your eye.  Sunlight scattered around the planet, reflected off the moon or an alien photon from a star trillions of miles away should make you look up and really marvel at the scale of it all.  And remember that even on the gloomiest, stormiest day, everything you can see, is a little bit of the sun shining back at you. 

One Comment

  1. That last sentence! Beautiful! This one gets me right in the feels – thanks so much for sharing this perspective. Seeing the night sky without light pollution is something I also have dreamed of my whole life…

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