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Bad Astronomy

June 22, 2006

Philip Plait wants to punch holes in all the ‘Bad Astronomy’ out there, from myths about the coriolis effect to the astronomical aspects of creationism to UFO’s and the moon-landing hoax.  To that end he’s created a website, www.badastronomy.com, he lectures at schools and research centers, and he’s written a book named, appropriately enough, “Bad Astronomy”.  I just finished reading it.

Plait is a solid scientist, an astronomer for the physics and astronomy department for Sonoma State University.  He’s very good with explanations…

‘Anything with mass has gravity.  You do, I do, planets do, a feather does.  I can exact a minute amount of revenge on Earth’s gravity knowing that I am pulling back on the Earth as well.  The amount I am pulling is pretty small, sure, but it’s there.  The more massive the object, the more it pulls.  The Earth has a lot more mass than I do (something like 78,000,000,000,000,000,000,000 times as much, but who’s counting?), so it pulls on me a lot harder than I do on it.

If I were to get farther away from the Earth, that force would weaken.  As a matter of fact, the force drops with the square of my distance; that is, if I double my distance, it drops by 2×2=4.  If I triple my distance, it drops by 3×3=9, and so on.

That does not mean that I feel one-quarter of the gravity if I climb a ladder to twice my height, though!  We don’t measure distance from the surface of the Earth, we measure it from its center.  A few hundred years ago, Sir Isaac Newton, the seventeenth-century philosopher-scientist, showed mathematically that as far as distance is concerned, you can imagine that all the mass of the Earth is concentrated into a tiny point at its center, so it’s from there that we measure distance…”
- Philip Plait, Bad Astronomy

Not to say I didn’t enjoy reading the book; I did.  But I do have a few quibbles over style.

First, he should remove remove the exclamation-point key from his computer, and give it to his wife under instructions to return it only when he can provide a good rationale for using it in the current sentence.  He tends to use exclamation points in places which are not points of exclamation.  I found it annoying, but then I am rather grouchy.

Second, he should hire an editor who isn’t in love with him.  When he says, “something like 78,000,000,000,000,000,000,000 times as much” it’s distracting and conveys less information (due to the difficulty in reading it) than saying “something like 7.8×1022 times as much” or “something like 78 sextillion times as much.”

Or when he says; “a few hundred years ago, Isaac Newton, the seventeenth-century philosopher-scientist” he should eliminate either “a few hundred years ago” or “seventeenth-century”. 

Third, and most important, he tends to go on for multiple paragraphs about how ridiculous some huckster’s fakery is, before explaining why it’s ridiculous.  He knows a lot of synonyms for “absurd”, and it just gets old. OK, Phil, you’re mad at the guy for being such a flim-flam; we get it.  Would you mind getting on with the debunking?

He writes exactly as one might lecture: “Let’s stay at the North Pole for a while (I hope you’re dressed warmly)”, “as a matter of fact”, etc.  There are lots of worse ways to write (and he is reputed to be an outstanding lecturer) and no style will appeal to everyone,  but what works in a lecture is often cumbersome on the printed page.

OK, so he isn’t Shakespeare; no one will confuse me with the Bard, either.  You shouldn’t let my stylistic natterings stop you from enjoying the book.  The two best things about the book are the infectious! enthusiasm! of its author, and the correctness of the explanations.  I’d like some of that fever to infect a few school boards.  After all, if you aren’t going to get the kids worked up about learning the truth, why have school?  Teachers, especially, should read the book, and better yet, invite Plait to speak or take a class full of kids to one of his events.

Categories: Books, Reviews
  1. Lucas
    July 2, 2006 at 00:47 | #1

    “The amount I am pulling is pretty small, sure, but it’s there.  The more massive the object, the more it pulls.  The Earth has a lot more mass than I do (something like 78,000,000,000,000,000,000,000 times as much, but who’s counting?), so it pulls on me a lot harder than I do on it.”

    Actually, you exert exactly the same amount of gravitational force on the earth that it does on you—“for every action there is an equal and oposite reaction.”  However, the Earth’s mass is so much greater than yours that the acceleration you experience is much greater than the Earth does.

    “A few hundred years ago, Sir Isaac Newton, the seventeenth-century philosopher-scientist, showed mathematically that as far as distance is concerned, you can imagine that all the mass of the Earth is concentrated into a tiny point at its center, so it’s from there that we measure distance…”

    The first statement is definitely false.  Point masses are *assumed* in Newton’s mechanics—Newton did not prove mathematically that they are a perfect approximation of reality.  First, he did not have access to the mathematics of vector fields to attempt such a proof, but also the proof would have failed.  Point masses are a very good approximation, especially when the masses are fairly evenly concentrated near that center, but they are not perfect.  Imagine a planet made of an incredibly strong material which has half of its mass concentrated in a spherical lump about the mass of Earth.  The other half of the mass is in the form of a 1mm thick rod extending for some substantial portion of a light year from the north pole.  If you stand on the planet, you will not be drawn to the center of mass of the planet (millions of miles away from you), but your feet will stick to the ground.

    Perhaps these are subtleties best left out of science books, but it seems like science writers shouldn’t simplify to the point of falsehood.

  2. Lucas
    July 2, 2006 at 00:58 | #2

    My GOOGLE assisted calculations indicate that the rod in the thought experiment would be about 3.6*10^10 lightyears long, or about twice the size of the observed universe if we assume the same density as the Earth.  Of course such a rod couldn’t really exist, but it shows why point masses are an imperfect approximation.

  3. July 2, 2006 at 09:43 | #3

    I think that once again, Plait is guilty of bad writing here.  He is probably referring to the gravitational acceleration of the two respective bodies, rather than the aggregate attraction between them.  He’s being unclear, which is functionally equivalent to being wrong when you’re trying to communicate something.

    I do believe you’ve got him on the “Newton mathematically proved” rap.

    I give him an A+ for good intentions and enthusiasm, and he’s probably a blast in his public demonstrations.  But I wish he would team up with a seasoned science writer. 

    Here’s what I wonder about the point-mass thingie:  isn’t proximity important?  When I am standing on the surface of the Earth, there’s a large percentage of the mass is off the axis of a straight line from my belly button to the center of the Earth.  It seems like what I perceive as “down” would be the high point on a curve representing directional acceleration.

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