Sunday night the Moon is 95 percent illuminated, with just five percent to go before sunlight touches every part that we can see. With just five percent unlit, you’d think that the Moon would get five percent brighter between then and Tuesday. But no, the Moon will grow 100 percent brighter: twice as bright. Why?
The cause is the Moon’s powdery surface. It reflects sunlight straight back toward its source, the way a movie screen’s image looks much brighter to those who are most in line with the projector. Even more importantly, the roughness of the lunar surface creates countless little shadows. Only when the Sun is shining straight down are these all “filled in.” Bottom line: You have to be between the Sun and Moon to see sunlight bounced most intensely to your eyes from the Moon, and this is precisely the geometry of the Full Moon that will happen on Tuesday.
Despite its brilliance, the Moon is not a good reflector of light – far from it. Its terrain reflects away just eight to 13 percent of incoming sunlight, making it as dark as asphalt. By comparison, the percentage of light reflected from Earth is about 38 percent, while Venus bounces away 76 percent. If a Moon-sized Venus sat at the Moon’s distance from us, it would appear seven times more brilliant than the Full Moon: enough to give us a blue sky.
Very few objects in the known universe are duller than the Moon, which looks bright only because it is so close and stands out against the even-darker background sky. But it would become no blacker if an ambitious developer paved its entire surface with asphalt and turned the Moon into a parking lot.
Other lunar oddities?
- The Moon is the only celestial body that moves through space its own width each hour (average speed: 2,287 miles per hour; diameter: 2,162 miles). That’s why solar and lunar eclipses take an hour to go from start to totality.
- The Moon is the only major satellite that doesn’t orbit its planet’s Equator. Instead, it ignores Earth’s tilt and revolves in the same plane as the planets – which is why it travels through the Zodiac.
- Like Mercury, the Moon stands “straight up” relative to the Sun. And also like Mercury, this lack of tilt allows depressions at the poles to remain permanently shadowed, keeping those regions cold enough to house millions of tons of ice.
- The Moon is lightweight, made mostly of a silicon/oxygen mix, like sand. In fact, the Moon is half oxygen!
- On its surface lies an odd baby-fine soil with a talcum-powder consistency. This “regolith” makes the Moon wonderfully smooth to the touch.
- The lunar core is solid: essentially one giant crystal. This causes our natural satellite to keep shaking whenever it’s struck by a large meteor. At such times the entire Moon rings for hours like an enormous gong.
- And it appears much smaller than people imagine. The number of Moons needed to fill the entire sky: 105,050.
Since we never step quickly from sunlight to moonlight, it’s hard to gauge the difference between them. Is the Sun a hundred times brighter than a Full Moon? Five hundred? Surprisingly, the Full Moon is 450,000 times dimmer than the Sun. But our nearest neighbor is still a thousand times brighter than the combined light of all the stars.