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SYFY WIRE Bad Astronomy

To Sail the Winding River of Light

By Phil Plait

Sometimes, when I daydream, I wonder what it would be like to float over the Earth, 400 kilometers above the ground, letting the view of our green and blue and brown world flow by beneath me.

And then I remember I donât have to dream about it. Humans already do this. And they can record their passage, sending the images back to us mortals forever bound to the surface. And when they do, for a moment, we fly with them.

This breath-taking photograph was taken by an astronaut on board the International Space Station on September 17, 2011, when the station was over the southern Indian Ocean, about halfway between Africa and Australia. [And oh, how you want to click that to embiggen it.]

Thereâs so much to see in this picture! The solar panels that power the station are on the right, and various other structures frame the picture. The exposure time was 1.3 seconds, long enough for a few stars to show up. The three stars in a row in the middle of the shot are Orionâs belt, and to the upper right of that you can see three fainter aligned stars marking his dagger (or so we astronomers like to tell you). If it looks funny to you, thatâs because it looks upside-down! To us Northern Hemisphereans, the dagger is below the belt, but when you go south of the equator, the directions flip. I saw this very thing visiting Australia a few years ago, and it was very disorienting, but amazing: proof positive we live on a spinning ball of mud whirling through space.

On the right, more or less in line with the Belt, you can see Sirius, the brightest star in the night sky. On the left is the large V-shaped Hyades star cluster that demarcates the head and horns of Taurus, the bull. On the lower right of the V is the star Aldebaran, a star that was once much like the Sun but is now nearing the end of its life. Itâs swollen into a red giant, more than 40 times the width of our Sun, its ruddy color obvious to the naked eye.

But as wonderful as the stars are, itâs the sinuous river of eerie and lovely green light across the Earthâs face that draws the eye. That glow marks the location where vast torrents of subatomic particles blown out from the Sun in its solar wind are channeled and funneled down by the Earthâs magnetic field, slamming into our atmosphere at high speed. The particles collide with atoms and molecules in the air and energize their electrons, either lifting them to a higher energy state or blasting them off their parent atoms/molecules completely. When the electrons jump back down to a lower energy state they release light, the color of which is determined by the particular kind of atoms and molecules. Oxygen glows green and red, while nitrogen emits blue, purple, and red. The collisions happen about 100 kilometers (60 miles) above the Earths surface, which becomes obvious when you look near the horizon, the edge of Earthâs disk. The aurorae are clearly well above the ground, hanging above the surface, but still well below the height of the station.

You can also see a thin brown-green arc parallel to the horizon. That's called the airglow, and the process that creates it is similar to the aurorae, but the culprit in this case is ultraviolet light from the Sun energizing molecules in the upper atmosphere during the day, which then slowly release that energy as light during the night.

What a thing it must be, to look out your window and see all these sights! I could never do this; I get sick to my stomach on a kidâs swingset, so astronautdom is well outside my own abilities. But weâre a diverse lot, we humans, some of us capable of withstanding the slings and arrows of spaceflight.

And actuallyâ¦looking at Orion, imagining him wrestling with Taurus as heâs sometimes depicted as doing, reminds me of another myth: that of Antaeus, a giant born of Poseiden and Gaia, who battled Hercules. Antaeus drew his strength from the ground, and was invincible as long as he was connected to the Earth. To defeat the giant, Hercules lifted him up, keeping him away from Mother Earth until he was too weak to fight.

That myth is commonly used as metaphor, sometimes to depict our attachment to home. But I wonder. When I see pictures like the one above, I think the myth got it exactly backwards: Space travel makes us stronger, not weaker. We are the Anti-Antaeus, gathering strength the more we leave Mother Earth.

Myths are stories, fanciful and fantasy. Journeying into space is real. The ancients thought it took the gods to lift up heroes into the sky, making them into the stars and constellations, becoming part of the sky itself. But the truth is, we did it ourselves.

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