Bad Astronomy. Misconceptions and Misuses Revealed, from Astrology to the Moon Landing 'Hoax'

September. Even better, the seasons are opposite in the northern and southern hemispheres; when it’s spring in one it’s fall in the other and vice versa. But people usually don’t think of these things. It’s too easy to simply accept what you’re told. This is extraordinarily dangerous. If you just assume without thinking critically that someone is right, you may be voting for the wrong politician, or accepting a doctrine that has a bad premise, or buying a used car that might kill you. Science is a way of distinguishing good data from bad.

Practicing science is wonderful. It makes you think about things, and thinking is one of the best things you can do.

2. Flushed with Embarrassment: The Coriolis Effect and Your Bathroom

It’s a pretty scene. Nanyuki is a small town situated just north of the equator where it cuts across Kenya in Africa. The town was founded early in the twentieth century, and still has something of a frontier feel to it.

It’s a frequent stop for tour buses on their way to nearby Mount Kenya. It has the seemingly mandatory gift and curio shops, but it also features a local man named Peter McLeary. As tourists gather around, McLeary shows them a demonstration they are not likely to forget. More’s the pity.

McLeary takes the tourists to a line drawn on the floor of an old burned-out hotel, and tells them that it’s the actual location of the equator. A glib speaker, he explains that water swirls down a drain clockwise north of this line and counterclockwise south of it, an effect caused by the rotation of the Earth.

He then goes on to prove it. He takes a small, roughly square pan about 30 centimeters across and fills it with water. He places some matchsticks in it so that his audience can see the rotation more easily. Walking to one side of the line and turning to face his audience, he pulls out a stopper, letting the water drain out. Sure enough, when he does this demonstration north of the equatorial line the water drains clockwise, and when he repeats the experiment south of the line, the water drains the other way. Proof positive that the Earth is spinning!

The demonstration is convincing, and McLeary has done it for many years, raking in tips from the credulous tourists. It has been seen by countless travelers, and was even featured on the PBS series Pole to Pole, in which former Monty Python silly man Michael Palin tours the world, taking in interesting sights. In this particular episode Palin watches McLeary do his thing and adds, “This is known as the Coriolis effect… it does work.” Actually, no, it doesn’t. Palin, and who knows how many tourists before and after him, are being taken in by a fraud. And it doesn’t end there. This hoary idea is used to explain why toilets flush in different directions in the northern and southern hemispheres, as well as the way northern and southern sinks and bathtubs drain. Many college students claim that their high school science teachers taught them this fact. The problem is, it’s no fact. It’s bad astronomy.

The Coriolis effect is real enough. By the 1800s, it had been known for years that cannonballs fired along a north-south line tended to deviate from a straight path, always landing west of their mark if fired toward the south, and east if fired to the north. In 1835 the French mathematician Gustave-Gaspard Coriolis published a paper with the unassuming title of, “On the Equations of Relative Motion of Systems of Bodies.” In it, he describes what has become known as the Coriolis effect.

Imagine you are standing on the Earth. Okay, that’s easy enough. Now imagine that the Earth is spinning, once a day. Still with me? Okay, now imagine you are standing on the equator. The rotation of Earth takes you eastward, and after a day you have swept around a big circle in space, with a radius equal to the Earth’s radius. On the equator, that means you have traveled about 40,000 kilometers (25,000 miles) in one day.

Now imagine you are on the north pole. After one day, you have rotated around the spot on which you are standing, but you haven’t actually gone anywhere. The north pole is defined as the spot where the Earth’s rotation axis intersects the ground, so pretty much by definition you don’t make a circle there. You just spin, making no eastward motion at all.

As you move north from the equator, you can see that your eastward velocity decreases. At the equator you are moving nearly 1,670 kilometers per hour (1,030 miles per hour) to the east (40,000 kilometers in 24 hours = 1670 kph). At Sarasota, Florida, at a latitude of about 27 degrees north, you are moving east at 1,500 kph (930 mph), and by the time you reach Wiscasset, Maine, at 44 degrees north latitude, you are moving east at only 1,200 kph (720 mph). If you brave the chill of Barrow, Alaska, you’ll be at latitude 71 degrees north and moving at a leisurely 550 kph (340 mph). Finally, at the north pole, you aren’t moving east at all; you just make your tiny circle without any eastward movement.

Let’s say you stop in Sarasota, which is a reasonable thing to do, given the climate there compared to Barrow. Now imagine someone on the equator due south of your position takes a baseball and throws it directly north, right toward you. As it moves northward, its velocity eastward increases relative to the ground. Relative to you, that baseball is moving 1,670 kph ? 1,500 kph = 170 kph (1,030 mph ? 930 mph = 100 mph) or so to the east by the time it reaches you. Even though the fastball is aimed right at you, it will miss you by a pretty wide margin! By the time it gets to your latitude, it will be a long way to the east of you.

That’s why cannonballs are deflected as they travel north or south. When they are first shot from the cannon, they have some initial velocity to the east. But if they are fired north, they reach their target moving faster to the east than the ground beneath them. The cannoneer needs to aim a bit west to compensate. The reverse is true if it is fired south; the cannonball reaches its target moving slower than the ground, and needs to be aimed to the east to actually hit the target.

In our baseball example above, the distances and times involved were large, letting the Coriolis effect gather some steam. In reality, it’s a tiny effect. Let’s say you are driving a car north at 100 kph (60 mph) in Wiscasset, Maine. The Coriolis effect deflects you by the teeny amount of 3 millimeters (0.1 inches) per second. After a solid hour of driving, that amounts to a deflection of only 10 meters (33 feet). You couldn’t possibly notice this.

Still, it is there. It’s subtle, but over long distances and large amounts of time it adds up. That can be a mighty sum, given the correct circumstances.

And those circumstances do arise. An area of low pressure in the atmosphere is like a vacuum cleaner, drawing in the surrounding air. Let’s take the simplified view that we are in the northern hemisphere, and assume that the air is coming in only from due north and due south. The air coming in from the south is moving faster to the east than the air near the center of the low-pressure system, so it bends to the east. Air moving from the north is moving slower than the air in the center of the system, and deflects west. These two deflections add up to a counterclockwise rotation to the low-pressure system. This is called a cyclonic system.

The opposite is true in the southern hemisphere. A low-pressure system will spin clockwise because air drawn in from the north will be moving faster to the east, and air coming in from the south will be moving slower. The spin is opposite from the northern hemisphere, and is called an anticyclonic system.

If the system is stable for a long time, days or weeks, it can grow massively in strength. Warm ocean water feeds the system, making it stronger. As the air gets closer to the center it moves faster, like an ice skater who spins faster when she draws in her arms. If the winds can gain in strength and blow at a hundred or more kilometers per hour, it becomes a hurricane (or a typhoon if it’s in the Pacific ocean).

The Coriolis effect is only significant over large distances. A hurricane is born when a low-pressure patch of air draws air in from higher and lower latitudes. Because of the Coriolis effect, in the northern hemisphere the air from the south moves east, and the air from the north moves west, causing a clockwise rotation.

All that, from that tiny deflection you can’t even feel in a car!

Does this sound familiar? Sure! It’s the same idea that Peter McLeary uses to explain why water swirls the way it does when he gives his demonstration in Kenya.

But there’s a problem: as we already saw, the Coriolis effect only produces a measurable effect over huge distances and long periods of time. Even the most decadent of bathtubs is thousands of times too small and drains way too quickly to ever be affected by it. It can be shown mathematically that random motions in your water are thousands of times stronger than the Coriolis effect, which means that any random eddy or swirl in the water will completely swamp it. If the water always drains one way from your bathtub, then it has far more to do with the