Golden age of lunar equilibrium
New Year’s Moon 2010, when reflected sunlight made the quarter-million-mile journey to Earth and was refracted through thin clouds above Brentwood, California.
Like an angel of heaven, she’s a creature of reflected glory; you can gaze on her and not be blinded. She’s a lesser power, yet she rules the domain of night unchallenged, delivering us from darkness but troubling our dreams. She can blot out the Sun or blush the color of blood. She has conjured images of werewolves and goddesses; fascinated ancient astronomers and enticed modern astronauts. Luna, Earth’s eternal consort.
In the course of countless solo night hikes, most guided by moonlight, I’ve seen Luna in myriad moods from myriad angles: the slenderest of crescents suspended featherlike in the delicate updraft of dawn, or as fragments of pale gold flashing through gaps in trees as I stride 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, Earth would be devoid of human life.
Our Moon is unique. Several other planets in our solar system are circled by moons (Jupiter’s number between 85 and 90), but none boasts a moon so large relative to the parent planet. And that’s good for us. Over the eons, our Moon’s mass has exerted a stabilizing force 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, more complex and 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 cold of space. Then it happens: Earth is sideswiped by a planetoid half its size, which shears off and spews into Earth orbit a huge glob of that magma mantle. The debris forms a ring, and through the force of gravity gradually coalesces into a sphere.
Moon over Murchio Gap, Mt. Diablo State Park, California.
In that original state, our Moon was the ultimate NEO (near-Earth object). Our 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: viewed from Earth, our Moon and Sun are roughly the same size, providing the awe-inspiring vision 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 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 snapped the first photos of the far side. In December of 1968, human eyes finally gazed at 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? Just as the Moon has stabilized Earth’s axis of rotation, Earth has stabilized the Moon’s period of rotation. As the eons rolled along, Earth’s mass slowed Luna’s rotation until it equaled her period of revolution. The Moon is now tidally locked (“phase-locked”) with Earth: it takes Luna 27.3 days to rotate once on her axis and 27.3 days to revolve once around Earth, preventing us earthbound Moon mavens from viewing the heavily cratered far side.
Mark your calendar for Saturday, October 28. In the San Francisco Bay Area, the full Moon rises at 6:11 p.m. and the Sun sets at 6:12 p.m. My advice as a friend: hike, drive or paraglide to the highest spot you can find and savor the spectacle: embers of Sun sinking in the west while the Moon, rising in the east, pales from peach to pearl to blinding white. A good way to celebrate the golden age of Luna.