Because some people still aren't convinced the Earth is round, its shadow on the moon will prove without a doubt that our planet is a sphere, said Eric Vandernoot, astronomy coordinator at Florida Atlantic University in Boca Raton.

"I occasionally have had people come to the observatory to debate the idea that the Earth is spherical and that gravity holds people on the Earth," he said. "Luckily, not too often. But they are out there."

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