Galaxies on Instagram: "On a clear, dark night with no light pollution, the human eye can see about 2,500 to 3,000 stars at once from any one location on Earth. That’s out of roughly 5,000 to 6,000 visible to the naked eye total (since half the sky is below the horizon). If you use binoculars or a telescope, that number jumps into the hundreds of thousands to millions, depending on the equipment and conditions. But with just your eyes, around 3,000 max is what you’ll see under perfect skies."

Hank Green on Instagram: "Does the first image of Earth prove that it’s flat?"