October 25, 2016

Pluto by Moonlight

Pluto by Moonlight

It’s Antarctic winter on Pluto. The Sun has not been visible for twenty years in this frigid south polar region; it will not shine again for another 80 years. The only source of natural light is starlight and moonlight from Pluto’s largest moon, Charon.

If you stood on the night region of Pluto at that moment – looking up at a distinctly gray Charon - it would appear seven times larger in the sky than Earth’s moon. Charon, although three billion miles from the Sun, is so close to Pluto and so ice-covered that it would be only five times dimmer than the full moon seen from Earth. At your feet, the icy surface – resembling a sooty snow bank - would be bathed in Charon’s faint glow. The area around you would be dim, but not so dark that you would bump into things.

On your moonlight stroll on Pluto you’d notice that your shadow, cast by Charon, is much less defined than your shadow from moonlight on Earth. A wisp of cloud might even pass in front of Charon as you look up.

If you stood on Pluto’s Charon-facing side – you would see Charon go through a cycle of phases during a “Pluto Day” - 6 days and 10 hours—but not the complete set of phases our moon displays to us on Earth. Seen from Pluto during that time, Charon would go from a wide crescent, to a “quarter moon,” then to gibbous (partway between quarter and full phases), and back again.

Image Credit: JHUAPL / SwRI
Explanation from: http://www.nasa.gov/image-feature/pluto-by-moonlight

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