The Earth spins once every 23 hours and 56 minutes in relation to the background stars. It takes 24 hours for the sun to return to the same spot in the sky.
Like you, I’m given to wondering about “what ifs” to better understand the assumptions we make about the world. One of my favorites is what if the Earth stopped rotating?
Let’s just say things would go sideways fast. Since the Earth spins us at 1,000 mph to the east, a sudden brake on its rotation would send everything not bolted to bedrock through the air in a terrifying tsunami of bricks, buildings, trees, people and cars. The deceleration alone would pulverize many common materials.
Picture a car traveling at 1,000 mph hitting a wall. That’s what we’re talking about here. Now imagine everything around you doing the same; the chaos and destruction would put the kibosh on civilization as we know it.
If the headlong flight of everything around you doesn’t do the trick, wind and water will take care of everything else. The atmosphere also shares in the Earth’s rotation, and since it’s not attached to anything, it’s free to move. Stop the Earth and suddenly you’ll have supersonic 1,000 mph winds clawing away at what little is left standing.
The same holds true for water. With 71% of Earth’s surface covered in water, 1,000 mph tsunamis would rise up over much of the planet’s landmass and scrub it to the nubs.
A small sampling of rotation speeds across the northern half of the globe. Illustration: Bob King
Depending where you live, the speed of your now flying car during this theoretical disaster would vary. Earth’s circumference is 25,000 miles at the equator and the planet rotates once in about 24 hours. If you could look down and see Earth spin, people at the equator would be scooting along at 1,041 mph (25,000 divided by 24). As you move north or south of the equator the distance around the Earth shrinks until you arrive at the poles where it’s zero. Since a smaller “circle of Earth” spins through the same 24 hours, folks north and south of the equator travel more slowly.
Here at 47 degrees north latitude in Duluth, Minn., my kitchen, computer and typing fingers are merry-go-rounding the planet at 708 mph. Things aren’t crashing into each other because everything around me partakes of the same speed so long as I don’t rush hot tea to my lips and cause a nasty spill. Essentially, the world appears at rest.
To find your own PBV (personal ballistic velocity) number during our hyper-emergency, multiply the speed at the equator by the cosine of your latitude. Don’t sweat cosines. Just go to Google and type in the word cosine followed by your latitude like this – cosine 47 degrees. Take that number and multiply it by 1,041 mph to find how fast you’re traveling. Here’s a table of sample latitudes:
* 0 degrees (equator) = 1,042 mph
* 20 degrees N or S = 978 mph
* 40 degrees N or S = 797 mph
* 60 degrees N or S = 520 mph
* 80 degrees N or S = 180 mph
* 90 degrees N or S (poles) = 0 mph
Only the poles stand out as potential places to avoid the worst of our sickening scenario. But not for long, as we’ll soon learn.
Assume for a moment you’ve just survived this worst catastrophe since that Mars-sized planet slammed the Earth 4.5 billion years ago liberating rocks that later coalesced into the moon. Once the smoke cleared and the wind died down, you’d notice a few oddities.
The sun stays up for about six months on a non-rotating Earth. Illustration: Bob King
Without rotation, one side of Earth would be in darkness, the other in sunlight. If you ended up on Earth’s sunny side at sunset, you’d be surprised to see the sun traveling backwards (from west to east) very slowly – about the width of your little finger a day. After approximately 182 days or half-a-year, it would finally set in the east followed by a couple weeks of twilight and then a night lasting nearly five months. If that sounds cold and dark it would be, since that’s pretty much what Antarctica experiences every year. After another couple weeks of twilight you’d be grateful to see the sun finally return again in the west.
Without rotation to provide the familiar 24-hour day-night cycle, we’d have to wait for Earth’s much more ponderous 365-day-long revolution around the sun to experience day and night. Our planet would now take a full year to do what it used to in a day. The pinkie-width daily movement of the sun is a reflection of Earth’s revolution.
At this point you might be wondering what else could go wrong if Earth stopped spinning. The Earth’s spin creates centrifugal force that causes its equator to bulge outward. Without rotation to maintain the bulge, Earth would become a near perfect sphere as equatorial waters flowed towards the poles. In their wake, we’d likely see a brand new equatorial supercontinent exposed.
The structure of the Earth including its interior solid core surrounded by the liquid outer core. The inner core is similar to the temperature of the surface of the sun: 10,800 F (6000 C). Credit: Wikipedia
Finally, let’s consider the Earth’s innards. The latest data show that our planet has a solid core of iron-nickel 1,500 miles (2,400 km) that spins in the same direction at nearly the same speed as our rotation. Assuming the core would keep on turning once the brakes were put on Earth’s turning, it would continue to spin, likely tearing the planet apart from the bottom up. You’d end up with a blazing ball of lava surrounded by rings made the former Europe, U.S. and all the rest.
OK, so let’s stop the core. Not a good idea. Spinning a big ball of iron-nickel helps to create a magnetic field around the planet that protects us from dangerous solar and cosmic radiation. Without it, we’d get fried from above. And worst of all, without a magnetic field, we’d have to kiss the aurora borealis goodbye … probably forever. That hurts, but by then Earth wouldn’t be any fun anymore anyway.
Nothing short of getting whacked by another planet, something that won’t happen anytime soon, would drastically change Earth’s spin. Meanwhile you and I will just keep going around in circles trying to make sense out of this crazy life.
Artist’s view of the early Earth still under bombardment by comets and meteorites some 4 billion years ago. The moon was closer to our planet then and rotated faster than it does today. So did the Earth. Credit: Dr. David Aguilar
Our pale blue planet started turning long ago when dust and gases orbiting the infant sun drew together under the force of gravity to form the seed that would later become Earth. As the material collapsed towards its center, it rotated faster and faster just as a skater does when she draws her arms in during a spin. It probably took around 100 million years (2% the age of the solar system) for the Earth to form through the gradual accumulation of smaller objects.
Earth began its existence with a much faster rotation than the current. Shortly after the moon formed some 4.5 billion years ago, a full day on the planet lasted just 5 hours – barely enough time to get out of bed, eat breakfast and go to work before the sun would set. Because of gravitational friction via the tides raised by the moon’s gravitational pull, our spin has been slowing down ever since. In 140 million years, a day will be 25 hours long.