The serenity of Pluto’s sunsets

Worlds with atmospheres look different from any other if seen from behind.  The atmosphere refracts sunlight, bending it around the limb of the world and transmitting it in a color that hides clues to its composition.  Standing on the surface of the Earth, we experience this in the way the Sun seems to slow down as it nears the horizon (it isn’t actually slowing; it’s just that as its light passes through more and more air, it is bent further and further – by the time you see it it start to slip behind the horizon, it’s actually been down below the real horizon for a while; the air is acting a bit like a periscope, letting you see around the horizon a little ways), the way the light lingers on for so long after sundown, the impassively rising softened shadow of the Earth as it shades from pink to blue, and the red colors we see so strongly at this time of day.  Astronauts see this from space, a bit at a time.  And when spacecraft are sent to distant worlds that have (or might have) atmospheres, they are always programmed to turn around in the shadow and look for the sun projected around by an atmosphere.  Earth, Venus, Titan, the gas giants, even Mars to some extent, and now Pluto.  And, in keeping with everything else on this mission so far, it looks unique in the solar system.  Layered, and very very blue:



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