The number 40,000 stood out to me because the Earth is roughly 40,000 kilometres in circumference. Of course, this is 40,000 miles, so it's roughly 1.6x the circumference of the Earth.

I don't really know what the circumference of the moon is. Or, at least I didn't. Combine the facts above with the ones in the article, and you discover the circumference of the moon is roughly 1/4 that of the Earth.