The Day the Moon Was Gone
We Probably Owe Our Very Existence to the Moon

The Day the Moon Was Gone
We Probably Owe Our Very Existence to the Moon

The Moon is in synchronous rotation: it rotates about its axis in about the same time it takes to orbit the Earth. This results in it nearly always keeping the same face turned towards the Earth.

The Moon used to rotate at a faster rate, but early in its history, its rotation slowed and became tidally locked in this orientation as a result of frictional effects associated with tidal deformations caused by the Earth.

Without the moon, Earth would be a very different and desolate place today––four hours of sunlight with pitch-black nights, steady 100-mph winds spawning giant hurricanes that last for months, and virtually no complex life forms, much less humans.

Safe to say, we probably owe our very existence to the moon. But what if it suddenly disappeared?

The Moon is Earth's only known natural satellite, the fifth largest satellite in the Solar System. It is the largest natural satellite of a planet in the Solar System relative to the size of its primary, having a quarter the diameter of Earth and 1⁄81 its mass.

The Earth-Moon system is unique in that the ratio of the mass of the Moon to the Earth is much greater than any other planet-moon ratio in the Solar System, and the Moon's orbit with respect to the Sun is always concave.

The Moon is the second densest satellite after Io, a satellite of Jupiter. It is in synchronous rotation with Earth, always showing the same face; the near side is marked with dark volcanic maria among the bright ancient crustal highlands and prominent impact craters.

It is the brightest object in the sky after the Sun, although its surface is actually very dark, with a similar reflectance to coal.

Its prominence in the sky and its regular cycle of phases have since ancient times made the Moon an important cultural influence on language, calendars, art and mythology.

The Moon's gravitational influence produces the ocean tides and the minute lengthening of the day.

The Moon's current orbital distance, about thirty times the diameter of the Earth, causes it to appear almost the same size in the sky as the Sun, allowing it to cover the Sun nearly precisely in total solar eclipses.

The tides on the Earth are mostly generated by the gradient in intensity of the Moon's gravitational pull from one side of the Earth to the other, the tidal forces. This forms two tidal bulges on the Earth, which are most clearly seen in elevated sea level as ocean tides.

Since the Earth spins about 27 times faster than the Moon moves around it, the bulges are dragged along with the Earth's surface faster than the Moon moves, rotating around the Earth once a day as it spins on its axis.

The ocean tides are magnified by other effects: frictional coupling of water to Earth's rotation through the ocean floors, the inertia of water's movement, ocean basins that get shallower near land, and oscillations between different ocean basins. The gravitational attraction of the Sun on the Earth's oceans is almost half that of the Moon, and their gravitational interplay is responsible for spring and neap tides.