If you don't know that the Earth is a sphere, wrongly believing our planet to be flat, don't tell everyone on your Twitter feed and definitely don't make a song about it, or Neil Degrasse Tyson might come after you and respond in kind.
Earlier this week, rapper B.o.B publicly questioned a spherical Earth, throwing his support behind flat Earth theory in a series of tweets and memes and suggesting a NASA cover-up.
Discounting any photo taken by a NASA spacecraft - an untrustworthy source, according to B.o.B - and setting aside any images captured by other space agencies around the world or photos taken by commercial satellites while we're at it, how do we know for fact that the Earth is spherical?
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The ancient Greeks figured it out 2,500 years ago without having to fly into space and take a snapshot. How hard can it be?
Pythagoras in 500 B.C. provides the earliest arguments for why the Earth is round. The moon, he noted, was also a sphere, so it would follow that the Earth is round as well.