|Image courtesy of Kevin Van Aelst|
This observation was originally made by astronaut Gerry Carr aboard Skylab, America's first space station. Earth's diameter is about 7,900 miles and its atmosphere is about 62 miles thick. This means the diameter of the Earth is about 127 times the thickness of its atmosphere! The ratio for a given apple is somewhere around 80 millimeters wide to a skin thickness of 1.1 mm (depending on the size of your apple). Using these dimensions, Earth's atmosphere is actually THINNER than the skin of an apple in comparison to the Earth and the rest of the apple. It seems the sky is not as limitless as we may have thought!
The full quote from Carr.
This blog did the calculations to back up Carr's observation.