The Bad Astronomer

Every January, professional astronomers converge on a medium-sized convention center for the annual meeting of the American Astronomical Society. This year, the good city of Atlanta (not so medium sized) was host to this event, and seeing as I had gone to graduate school in Atlanta, I was looking forward not only to catching up on all the cutting-edge astronomy that would be presented at the convention, but also to re-connecting with old friends.

During the opening night reception, which invariably features reams of graduate students descending on the small buffet lines, I caught sight of one of my favorite people, Phil Plait, a.k.a. the Bad Astronomer.

Not that Phil is actually a bad astronomer. He's a professor at Sonoma State University, and although I've never been there, teaching astronomy in Sonoma sounds like a pretty good deal to me. But aside from his academic duties, Phil provides a monumental service to the space-science community, in the form of his website, essays, and book, all called "Bad Astronomy."

In these works, Phil takes a good-humored but rigorously scientific look at all different kinds of conspiracy theories and pseudo-science that seem to work their way into the public consciousness. As an astronomer working in public outreach, I often get questions from people who want to know why NASA faked the Moon landings (how else can you explain why there are no stars in the sky, or why the astronaut's shadows aren't all parallel?) or whether the Earth is at risk of being ripped apart by gravity when all the planets line up on the same side of the Sun. And honestly, I find myself at a bit of loss. To simply dismiss these questions as stupid makes me seem at best an arrogant scientist, and at worst, part of the "conspiracy" myself. So I fire up Phil's website, www.badastronomy.com.

What I really love about Phil's stuff is that he does the math. Take as an example the concern caused by planetary alignments, when some or all of the planets line up on one side of the Earth. Every few years, when a particularly good alignment is coming up, doom-sayers start coming out of the woodwork, claiming that the increased gravity or tidal forces will cause earthquakes and tsunamis, or even rip the Earth apart.

Is this possible? To me, the simplest counter-argument is that this must have happened in the past many, many times, and we're still here. Set nine planets orbiting the Sun, and every couple hundred or thousand years, they're bound to line up to some degree. Doesn't seem to have destroyed the Solar System yet. But if that doesn't seem qualitative enough to you, check out Phil's reasoning: he calculates (and the math is all there on his website), that the combined gravitational pull of all the planets is slightly less than 2% of the Moon's gravitational pull on us.

Well, is there a chance that even that amount of variation will affect the Earth? This is highly unlikely, as Phil points out, as the Moon's gravitational pull naturally changes much more than that in the course of a single month:

"Think of it this way: the Moon orbits the Earth in an ellipse, which means that sometimes in its orbit it is closer to the Earth than others. At perigee, or closest approach, it is about 363,000 kilometers away, and at apogee, or farthest point, it is about 405,000 kilometers away. If you use these numbers like we did above, you see that the Moon's own gravitational effect on the Earth fluctuates by about 25% every orbit! The Moon orbits the Earth in about a month, incidentally, so it goes from apogee to perigee every two weeks. So every 14 days we see a change in gravitational effects from the Moon more than 10 times greater than all the other planets combined!"

There's lots of other amusing debunkings to be found too. Supposedly, draining sinks are affected by the Coriolis Force, a rotational force caused by the Earth spinning on its axis. This force is indeed responsible for weather patterns being different in the two hemispheres, most obviously in the fact that low pressure systems rotate in a counter-clockwise direction in the Northern hemisphere, and clockwise in the South. Sinks are, in effect, small low-pressure systems, but they are much too small to feel this effect, and the water drains out of them far too rapidly. The direction that water spins as it drains away is much more effected by the shape of the sink basin or what motions in the water have been introduced ahead of time by, say, washing the dishes.

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