2016-07-06

How large is Charon at Pluto's sky?


What does it mean when scientists say, Charon was more than seven times larger in Pluto's sky than the Moon is in the sky of Earth? This direct comparison takes the very same setting on Earth, in Antarctica, and in the lower image relocates it into the Western "tail" of the Cthulhu Regio where Charon is still low above the horizon. 

In chapter 7 of "Pluto & Charon - The New Horizons spacecraft at the farthest worldly shores", the scene shown in the lower image is described like this:


What a sight would that be if Captain Future steered his spaceship down to the Sputnik Planum and headed westwards? On his ship races above the inviting broad nitrogen surface; then he is forced to pull steeply up when the icy islands of Baré Montes and the coastal line rising thousands of metres high behind come into view. Soon, the infinitely sombre ridges of the Cthulhu Regio march along beneath the ship. Just here and there, fresh ice glaciers flash on peaks like dewdrops. Faint sunlight just about manages to reveal the colour of the soil. it is dyed with dimly red tholin: a battlefield flooded under clotted blood, Yuggoth rather than Pluto.

   Suddenly an ashen dome looms forth behind the mountains. It grows to a disk and eventually withdraws from the western horizon, hugely blown up. This is Charon, Pluto’s repulsive brother. Seven times wider than Earth’s full moon it creeps up the sky, and no man in the moon smiles down from there. Ghastly is indeed the light cast by this dreadful orbiting giant. Not just dead it looks but murdered: Deep chasms cleft it apart from one side to another like a skull cloven by an axe. As if the blood from Cthulhu’s battlelands had gushed so high that it even stained the satellite, another clotted spot spreads twilight-red across its apex: a Death-star that Lovecraft himself must have made up!

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