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

blame the skies. The May 2000 planetary-alignment-disaster-that-wasn’t spawned a whole cottage industry of gloom and doom, but, like all signs from the sky throughout history, it turned out to be just another false alarm. As with most superstitions, the rational process of the scientific method came to the rescue. To find out how, let’s take a look at what an “alignment” really is.

All the planets in the solar system, including the Earth, orbit the Sun. They move at different speeds, depending on how far they are from the Sun. Tiny Mercury, only 58 million kilometers from the Sun, screams around it in just 88 days. The Earth, almost three times as far, takes one full year — which is, after all, how we define the year. Jupiter takes 12 years, Saturn 29, and distant, frigid Pluto 250 years.

All the major planets in the solar system formed from a rotating disk of gas and dust centered on the Sun. Now, nearly 5 billion years later, we still see all those planets orbiting the Sun in the same plane. Since we are also in that plane, we see it edge-on. From our vantage point, it looks like all the planets travel through the sky nearly in a line, since a plane seen edge-on looks like a line.

Since all the planets move across the sky at different rates, they are constantly playing a kind of NASCAR racing game. Like the hands of a clock only meeting every hour, the swifter planets can appear to “catch up” to and eventually pass the slower-moving ones. The Earth is the third planet out from the Sun, so we move in our orbit faster than Mars, Jupiter, and the rest of the outer planets. You might think, then, that they would appear to pass each other in the sky all the time.

However, the planets’ orbits don’t all exist perfectly in the same plane. They’re all tilted a little, so that planets don’t all fall exactly along a line in the sky. Sometimes a planet is a little above the plane, and sometimes a little below. It’s extraordinarily rare for them to actually pass directly in front of each other. Usually they approach the same area of the sky, getting perhaps to within the width of the full Moon, then separate again. Often they never even get that close to each other, passing many degrees apart. For this reason, surprisingly, it’s actually rather rare for more than two planets to be near each other in the sky at the same time.

Every so often, though, it does happen that the cosmic clock aligns a bit better than usual, and some of the major planets will appear to be in the same section of the sky. In 1962, for example, the Sun, the Moon, and all the planets except Uranus, Neptune, and Pluto appeared to be within 16 degrees of each other, which is roughly the amount of sky you can cover with your outstretched hand. Not only that, but there was also a solar eclipse, making this a truly spectacular event. The Moon and the Sun were as close as they could possibly be, since the Moon was directly in front of the Sun. In the year 1186, there was an even tighter alignment, and these planets could be contained with a circle just 11 degrees across.

On May 5, 2000, at 8:08 a.m. Greenwich Time, the planets Mercury, Venus, Mars, Jupiter, and Saturn were in very roughly the same section of the sky. Even the new Moon slid into this picture at that time, making this a very pretty family portrait indeed, although it was a bit of a dysfunctional family. This particular alignment wasn’t a very good one, and even if it had been, the Sun was between us and the planets like an unwelcome relative standing in front of the TV set during the football playoffs.

The fact that this wasn’t a particularly grand alignment is easy to show. The planets involved were within about 25 degrees of each other. That’s half again as far as the 1962 alignment, and more than twice as bad as the one in 1186. Both of these years, it should be noted, are ones in which the Earth was not destroyed. As a matter of fact, there have been no fewer than 13 comparable alignments in the past millennium, and in none of them was there any effect on the Earth.

Still, this hardly even slowed the doomsayers down. The combined gravity of the planets, they claimed, was still enough to destroy the Earth. Since we’re still here, we know that wasn’t true. Still, it pays to look at this a little more carefully.

The force of gravity is overwhelming in our daily lives. It keeps us stuck to the Earth unless we use tremendously powerful rockets to overcome it. Gravity is what holds the Moon in orbit around the Earth, and the Earth around the Sun. It makes parts of us sag as we get older, and even manages to keep the highest vertical leap of the greatest basketball players in the world under a measly meter.

But gravity is also mysterious. We cannot see it, touch it, or taste it, and we know that the math involved in predicting it can be complicated. So it’s easy — and all too human, I’m afraid — to assign all sorts of powers to gravity without really understanding it. In a way, understanding the effects of gravity is like a prize fight: science and its retinue of observations, facts, and math versus our superstitions, emotions, and the human power to jump to conclusions without much evidence. Which side will win the day?

Let’s take a quick look at what we know about gravity: for one thing, it gets stronger with mass. The more massive an object is, the stronger its gravity. From a kilometer away, a mountain has more of a gravitational effect on you than, say, a Volkswagen.

However, we also know that gravity gets weaker very quickly with distance. That Volkswagen may be a lot smaller than the mountain, but its gravity will actually overwhelm the gravity of the mountain if the car is close and the mountain far away.

It’s all relative. Indeed, the planets are massive. Jupiter tips the scales at over 300 times the Earth’s mass. But it’s far away. Very far. At its absolute closest, Jupiter is about 600 million kilometers (400 million miles) away. Even though it has 25,000 times the Moon’s mass, it is nearly 1,600 times farther away. When you actually do the math, you find that the effect of Jupiter’s gravity on the Earth is only about 1 percent of the Moon’s!

Despite the old saying, size doesn’t matter; distance does.

If you add up the gravity of all the planets, even assuming they are as close to the Earth as possible, you still don’t get much. The Earth’s tiny little Moon exerts 50 times more gravitational force on us than all the planets combined. The Moon is small, but it’s close, so its gravity wins.

And that’s true only if the planets are lined up as close to the Earth as they can get. As it happens, on May 5, 2000, the planets were on the far side of the Sun, meaning that you need to add the diameter of the Earth’s orbit — another 300 million kilometers (185 million miles) — to their distances. When you do, the combined might of the planets is easily overwhelmed by the gravity of a person sitting next to you in that Volkswagen. Sorry, doomsayers, but round 1 of this fight goes to science.

Usually at this point I am challenged by some people who say that it isn’t the gravity of the planets that can cause damage, it’s the tides. Tides are related to gravity. They are caused by the change in gravity over distance. The Moon causes tides on the Earth because at any moment one side of the Earth is nearer the Moon than the other. The side nearer the Moon therefore feels a slightly higher gravitational force from the Moon. This acts to stretch the Earth a tiny amount. We see this effect as a raising and a lowering of the sea level twice a day, which is what most people normally think of as tides.

Earthquakes are caused by the movement of huge tectonic plates that make up the Earth’s crust. They rub against each other, usually smoothly. However, sometimes they stick a bit, letting pressure build up. When enough pressure builds up, the plates slip suddenly, causing an earthquake. Since tides can stretch an object, it’s reasonable to ask whether tides can trigger earthquakes. Are we still doomed?

Happily, no. When doomsayers bring up tides, they are shooting themselves in the foot. The force of tides fades even faster with distance than gravity. If the force of gravity on Earth is piddly for the planets, then tides are even weaker. Comparing the Moon, again, to all the combined might of the planets, we find that the Moon has 20,000 times the tidal force of all the other planets in the solar system, even at their closest approach to the Earth. Remember, in May 2000 the planets were as far away as they possibly could be. The tidal force was so small that even the finest scientific instruments on the planet were not able to measure it. Round 2 of the fight goes to science as well.

Math and science show pretty definitively that the gravity and tides of the planets are too small to have any effect on the Earth. However, it would be foolhardy to assume that emotions are swayed by logic. In one sense, the side of science is lucky: since the planets were all on the far side of the Sun, we had to look past the Sun to see them. That means they were only up during the day, when they are practically invisible. It would not have helped the situation if people could actually look up at night and see the planets approaching each other, even if it were a pretty weak grouping.

Still, even armed with hard numbers, it’s always an uphill fight to battle the doomsayers. There were a lot of people out there trying to make money by scaring people about the alignment. Certainly some of these folks were honest, if misguided. Richard Noone wrote a book about the alignment, 5/5/2000 Ice: The Ultimate