Saturday, January 24, 2015

What if the Moon suddenly disappeared?

What if we had no Moon?
Or what if the we had a Moon like we do now and it suddenly disappeared?
Find out what would happen.

1.) There’d be no such thing as eclipses on Earth.
Without the Sun, Moon and Earth, there would be no eclipses. The Sun is constantly shining on Earth, casting a shadow for over a million miles (and over a million kilometers) in its wake. Yet without our Moon — just a few hundred thousand miles (or kilometers) away — there’d be no object that would pass through the Earth’s shadow; there’d be no lunar eclipses.
There’d also be no solar eclipses: no annular, partial, or total eclipses. The Moon’s shadow is almost exactly equal in length to the Earth-Moon distance; without the Moon, no shadow, and no disc to block the Sun’s disk. The next largest object that can pass in between the Earth (after the Moon) is Venus, and while it’s incredibly cool when that happens, that’s the closest we’d get to an eclipse without the Moon.

2.) Our tides would be tiny in comparison to what they are now, and they’d be dominated by the Sun.
Although the Sun is some 400 times larger (in diameter) than the Moon, it’s also, on average, about 400 times farther away. This explains why they appear about the same angular size from Earth. But the Sun is only about 27 million times as massive as the Moon.
Why in the world would I say “only” there? Because it would have to be about (400)3 times the mass of the Moon, or 64 million times its mass, in order to have the same effect on Earth’s tides as our small, lunar neighbor. As it stands, tides from the Sun are only about 40% as strong as tides from the Moon. When the Sun and Moon line up in either the “new” or “full” Moon phases, we get spring tides, 140% as large as a typical tide, and when they’re at right angles, we get neap tides, only 60% as strong as a standard tide.

3.) Nights would be much, much darker than we’re used to.
If you’ve ever been outside in the wilderness on a totally moonless night, without any artificial light, you probably noticed two things. First, the night sky is absolutely breathtaking; you can see thousands upon thousands of stars, the plane of the Milky Way, and even dozens of extended, deep-sky objects with your naked eye alone. And second, you can’t see a damned thing in front of your own face.
The Sun is much, much brighter than the Moon; the full Moon is just 1/400,000th as bright as the daylight Sun. Yet Venus, the next brightest object in the night sky, is only 1/14,000th as bright as the full Moon!
Image credit: Paul Kinzer of Cambridge University Press.
We have pretty decent night vision, so long as the Moon is out. But without it, our night vision is, well, not very effective, as anyone who’s been camping without a headlamp or working flashlight can testify. It’s probably safe to say that vision would have evolved somewhat differently without the Moon, and that our nights would provide us with a wildly different world to experience.
But that wouldn’t be the biggest difference, not by a long shot.

4.) A day on Earth would be much, much shorter; only about 6-to-8 hours, meaning there’d be between about 1,100-1,400 days in a year!
Our 24-hour-days may seem like they don’t change from one year to the next. In reality, the change is so tiny that it took centuries to perceive, but the Earth’s rotation slows down ever so slightly over time, thanks to the tidal friction provided by the Moon. The slow-down is very, very slow (on the order of microseconds-per-year), but over millions and even billions of years, it adds up!
In about 4 million years, we’ll no longer need leap years to keep our calendars on track. If the Sun would live an infinite amount of time, the Earth would eventually slow down and become tidally locked to the Moon, the same way the Moon is locked to us and always shows us the same face. Instead of 24 hours, a day would last for some 47 current Earth days. (In reality, the Sun will end its life long before that happens, so no worries there.)

Image credit: Fahad Sulehria of

But in the meanwhile, we can use what we know to extrapolate backwards in time, and we find that in order to get a 24 hour day today, the Earth had to have been spinning much faster in the past: about three-to-four times as fast more than four billion years ago! If we didn’t have a Moon — if we never had our Moon — the day would be much, much shorter than it is today, and our planet would have a larger equatorial bulge, much more flattened poles, and over 1,000 days in a year!

5.) Our axial tilt would vary tremendously over time!
You probably learned that the Earth rotates on its axis, tilted at about 23.5 degrees relative to its orbital plane around the Sun. This is true! But did you ever stop to think what keeps the Earth from changing the tilt of its axis-of-rotation? The same way a spinning top not only precesses but also exhibits more complicated motion over time (some of which you may know as nutation), an entire planet can do this, too. Mars is a perfect example: currently tilted at about 24 degrees relative to the Sun, we know that its axial tilt varies from about 15 degrees to about 35 degrees over time!
Thanks to our Moon, our axis stays tilted between 23 and 26 degrees over time, even over hundreds of millions of years! But without our Moon, there would be nothing preventing catastrophic shifts in our rotational axis. It’s probable that sometimes, we’d be like the planet Mercury, orbiting in the same plane as our rotation, and having practically no seasons due to our axial tilt. At other times, we’d possibly be as extreme as Uranus, rotating on our side like a barrel, having the most extreme seasons imaginable! So the next time you take our Moon for granted, think about how different life would be — and how different the entire history of life on Earth would have been — if we didn’t have our Moon.

Article originally published on ScienceBlogs  []

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