NASA astronaut Karen Nyberg snapped this photo of the Great Lakes while orbiting over North America in the International Space Station.

The world's largest group of freshwater lakes, lakes Superior, Michigan, Erie, Huron and Ontario together contain just over 20% of the world's fresh surface water. That percentage can be a little tough to fathom, but, then again, it's important to remember that there's not nearly as much water on this rock (fresh or otherwise) as many of us assume; Jupiter's moon Europa, for example, which is waaaay smaller than Earth, actually has more of the stuff than we do.

[Karen Nyberg via Chris Hadfield]