Looks almost like a plague spreading across the surface. Of course thats not what it is. But it looks like it. Light is all spread out on the moon
as it shown on the pic, however somehow the dark areas are absorbing it, instead of revealing itself.
They're called maria and most likely formed billions of years ago when the Moon was still
molten in the center. Something large enough hit it, causing it to crack open, and molten rock flowed out and covered the surface. This left it dark
and flat. Despite this appearance though, it's still heavily cratered.
It was a pretty long time ago. Back then the interior of the moon was mostly still warm and lava-ish. It's called mare because in latin it means
"sea". People in the old days thought it was actually some sort of lunar ocean.
I suppose it was an ocean. An ocean of lava, that is.
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