Here, he lets the (obviously photoshopped) photo speak for itself. The major claim in flat Earth theory, of course, is that it is flat. During a normal lunar eclipse, we look to the sky to see the moon go completely dark — a consequence of the Earth’s shadow blocking light from the sun from reaching the moon. This is possible because the Earth is both spherical and huge. If the Earth was flat, the shadow it would cast on the moon’s surface when it got between the sun and the moon would, in turn, look flat, as it does in Tyson’s photo.
This, obviously, is never going to happen.
Tyson’s tactic is reminiscent of the quippy clapback fellow science communicator Bill Nye gave to flat-Earthers in April, which also invoked the use of images to prove that the Earth is not flat.
“Hey, man on the internet, why don’t you drive to the edge of the Earth and take a picture? Then post it. Drive to the edge of the Earth. We’ll be here,” he said.