When it comes to the Moon, I can’t claim objectivity. In the course of roughly 200 solo night hikes, most guided by lunar light, I’ve seen the Moon – as I might see an old friend or lover – in countless moods from countless angles: the slenderest of crescents suspended featherlike in the delicate updraft of dawn, or as fragments of pale gold flashing randomly through gaps in trees as I run through the forest. I’ve seen her as a pearl glowing from the Milky Way’s river bed as clouds flow past her like leaves caught by the current. And I’ve seen her in eclipse, an angry queen robed in red, majestic and terrible.
No matter your take on the Moon – adoration, trepidation or indifference – consider yourself lucky she’s up there. Without the Moon in our equation, we’d be inhabiting a radically different Earth.
Our Moon is unique. Several other planets in our solar system are circled by moons (Jupiter’s number 63), but none boasts a moon so large relative to the parent planet. And that’s a good thing for us. Over the eons, the Moon’s mass has exerted a stabilizing effect on Earth’s 23½-degree axis of rotation. Without that consistent tilt, Earth would resemble Mars, wobbling like a top in collapse. Earth’s axis wobbles only slightly, allowing our planet to develop consistent climate patterns that make possible the development of larger and more complex (and thus more fragile) organisms – organisms like you and me.
The Moon hasn’t always been a pearlescent orb subtly gracing our sky. Fast rewind 4½ billion years: Earth is a red planet, not blue; a molten globe seething in the blackness of space. Then it happens: Earth is sideswiped by a planetoid half its size, which shears off and carries out into Earth orbit a huge glob of that magma mantle. The debris forms a ring, and through the alchemy of gravity gradually coalesces into a sphere.
In that original state, the Moon was the ultimate NEO (near-Earth object). The modern-day Moon orbits Earth at a distance of about 240,000 miles. The primordial Moon’s distance from Earth was a scant 12,000 to 18,000 miles. Imagine the Moon 15 times larger in the sky than she appears today.
But nothing in the universe stands still. In the ages since that colossal impact, the distance between Earth and Moon has been increasing. Right now is a good time to be alive: among other benefits, Moon and Sun are roughly the same size as viewed from Earth, providing us the awe and wonder of the solar eclipse. Eventually the receding Moon will appear smaller than the Sun, and the solar eclipse will be a vague memory buried deep in human DNA.
One image buried deep in our DNA is the face of the Moon – “the Man in the Moon.” Since our ancestors first looked up at that haunting image in the night sky, we’ve seen only one hemisphere of our planet’s satellite – what we call the “near side” – right up until A.D. 1959, when unmanned spaceships took the first photographs of the far side. In December of 1968, human eyes finally gazed down onto the far side as the Apollo 8 astronauts made the first manned lunar orbit.
Ever wonder why only one side of the Moon faces Earth? Well, just as the Moon has helped stabilize Earth’s axis of rotation, Earth has helped stabilize the Moon’s period of rotation. As the eons rolled along, Earth’s mass slowed the Moon’s rotation until it equaled her period of revolution. The Moon is now tidally locked (“phase-locked”) with Earth: it takes the Moon 27.3 days to rotate once on her axis and 27.3 days to revolve once around Earth, preventing earthbound Moon mavens from viewing the heavily cratered far side.
Early risers should consider themselves fortunate. This weekend, a sliver of crescent Moon will hover low in the east at dawn. Set your alarm a few minutes early, step outside and enjoy the spectacle of “earthlight”: the light of the pre-risen Sun caroming off our planet and flooding the entire lunar disc with a muted radiance.
If you’re thinking it’s crazy to roll out of bed early on Saturday, I’m thinking: Exactly – it’s the golden age of Luna. Earth’s Moon. A good time for lunacy.