“I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn’t feel like a giant. I felt very, very small.” -Neil Armstrong
The full Moon is undoubtedly bright. As viewed from the Earth’s surface, it’s the second brightest object of all, after the Sun, and is more than 1,500 times brighter than Venus. In fact, the full Moon is over 40 times brighter than the entire rest of the night sky combined, and can outshine even a big city when seen right next to one.
The rising full Moon and the city of Chicago, as viewed over Lake Michigan from Northwestern University’s campus. Image credit: colinbrownell of flickr.
But the Earth has the Moon beat on the only two intrinsic properties that matter: size and reflectivity. The much larger size of Earth means that a “full Earth” as seen from the Moon has 13 times the surface area as the full Moon as seen from Earth. But on top of that, the Moon, as bright as it appears in the sky, is actually a relatively dull grey in color, more similar to charcoal than it is to a snowy white. The Earth, on the other hand, has icecaps, clouds, and highly reflective continents, particularly where deserts are involved.
When a view of the Earth includes large amounts of cloud cover, the southern polar cap and large deserts over land, its high reflectivity can make it up to 55 times brighter than the full Moon. Image credit: NASA / Apollo 17.
So how bright is the Earth as seen from the Moon by comparison, and what does this tell us about these worlds? Find out on this edition of Ask Ethan!