Starts With A Bang

It’s NEVER Night on the Moon!

Ignignokt: Well well, I know that. I said that, but it’s his nap time now.
Err: ‘Cause he like, sleeps during the day.
Ignignokt: But at night he feeds.
Err: And it’s always night on the Moon!
Ignignokt: Don’t f*** with me, Err.” –Aqua Teen Hunger Force, Moon Master

Ahh, the Moon. The brightest object in our night sky is familiar to all inhabitants of Earth, and during its full phase, easily outshines everything else in the night sky, combined.

Image credit: Furious Photos -- Amazing pictures by a delusional hack.

Capable of casting strong shadows, and easily giving off a light that’s bright enough to read by, the Full Moon brings a great deal of illumination to an otherwise dark night sky. In fact, not only is a sky with a Full Moon 40 times brighter than a moonless sky, but the Full Moon creates as much light pollution as some of the most impressive cities on Earth!

Image credit: Flickr user colinbrownell, of the Full Moon and Chicago, from Northwestern U.

Even though the Sun, itself, is 400,000 times brighter than the Full Moon, the Full Moon is nearly 2,000 times brighter than the planet Venus, the next brightest thing in the night sky, and millions of times brighter than the dim stars you’ll see on a moonless night.

Image credit: Nicko Margolies of Nicko's Big Picture.

The Full Moon as seen from Earth is even brighter than the Sun as seen from the farthest known Kuiper-Belt Object at aphelion.

But, as you’ve no doubt noticed, it’s always the same side of the Moon that faces us. Even though there’s a slight variation in the face of the Moon that’s illuminated due to the orbital mechanics of the Sun-Earth-Moon system, we can always see nearly the same 50% of the Moon from Earth.

Image credit: Lunar libration, from wikimedia commons user Tomruen.

And if we can see them, then they can see us. From the point of view of someone on the side of the Moon that always faces Earth, they can see the Earth 100% of the time! Even when that portion of the Moon is experiencing “lunar night,” the 14 days out of the month where the Sun doesn’t shine on that portion of the Moon.

Image credit: HowStuffWorks, from the article of Craig Freudenrich, Ph.D.

The far side of the Moon (often incorrectly called the dark side; it’s just the side facing away from Earth) can never see the Earth. In fact, when orbiting spacecraft circling the Moon come from the far side back to the near side (the Earth-facing side), that’s when an Earthrise occurs over the Moon.

Image credit: NASA / Apollo 8 / Bill Anders.

From the middle longitudes on the Moon — those areas that are illuminated from the first quarter phase to the last quarter phase — the lunar “day” (when the Sun is out) corresponds to the smallest phases of the Earth. From these locations, when it’s lunar “night,” the Earth will always appear in at least a 50% phase.

Edited screenshot from the animation of lunar libration, above.

While the Full Moon might be incredibly bright — like I said, nearly 2,000 times brighter than Venus at its brightest — the Full Earth as seen from the Moon is as bright as thirteen Full Moons, meaning that there will be plenty of light on the Moon when the Sun’s not out, even if there’s no heat.

Image credit: Japan Aerospace Exploration Agency, JAXA / NHK, Kaguya (Selene).

You already know this, because when the Moon is just a thin crescent from Earth, you can still see the remainder of the Moon ever so faintly!

Image credit: Richard Bosman, from the Netherlands.

This is due to the reflected sunlight bouncing off of the Earth and striking the Moon; it’s strong enough to illuminate the Moon as seen from Earth! We call this light Earthshine, and it’s so bright that even a quarter-phased Earth (as seen from the Moon) is brighter than the Full Moon as seen from Earth!

So a huge area on the Moon — nearly the entire side that’s visible from Earth — never experiences a night as dark as the least dark night on Earth!

Well, with one exception…

Image credit: JAXA / NHK, Kaguya / Selene, of a lunar eclipse as the Earth rises over the lunar limb.

During a lunar eclipse! So the Moon has its own version of night and day, but for the 50% of the Moon that faces us, night is a whole lot brighter than we’ve ever experienced!