This meme has been circulated on Facebook over the past few weeks:
I totally approve of the sentiment, which is to mock superstition, in general, and especially the kind of superstition that puts trust in - and gives credit to - celestial bodies for influencing events that they couldn't possibly influence. (In this respect, it is also a somewhat more veiled attack on astrology and theism.) It can be fun to poke fun at people for believing ridiculous things that defy explanation or imagination; it's even funnier to poke fun at them for believing in the power of something that is long-dead. Funny, snarky stuff.
There's a problem with the message itself, though. Three, actually.
The first, which occurred to me immediately and I've seen repeated widely, is that stars don't live for millions of years - they live for billions of years. If it only ("only") took millions of years for an individual star's light to reach us on Earth, and it's not obviously in its death throes, (which could still constitute millions of years) it's almost certain that the star is still there.
The second problem, which I had to look up to confirm, is that our eyes can't actually perceive stars that are millions of light years away. (Most of us can faintly see the Andromeda Galaxy, which is 2.5 million light years away, but only as a blur of light. Not as distinct stars.) The Milky Way Galaxy is, in fact, only (again, "only") about 100,000 light years in diameter. And our eyes? Someone with perfect eyesight will struggle to see a star in Cassiopeia that's 16k light years. (A more typical pair of eyes can only see stars that are about 5k light years away.)
|The Andromeda Galaxy - all one trillion stars of it - is 2.5m light years away,|
and looks about as bright as a satellite.
The third problem? Another more obvious one: when we wish upon stars, that "star" is typically of the shooting-star variety. Which isn't a star - it's a piece of space debris burning up in the atmosphere. So, yes, by the time you finish your wish that shooting star has been totally burned up. That part's right. But you're also seeing it in real-time. So, again, the joke doesn't work.
So, what we're left with is a little meme about how the superstitious are ignorant of astronomy... but it's only funny if its readers' are similarly ignorant of astronomy. (Irony!)
On Facebook, a friend argued that the factuality of the joke wasn't important, because he appreciated the sentiment. (ie. The comforting feeling of superiority generated by the comedy.) I probably couldn't disagree more - the sentiment is empty precisely because the joke is entirely untrue. And I'd imagine, in fact, that the sorts of people who believe in astrology would offer up the exact same argument in support of their beliefs - it doesn't matter if their superstitions are scientifically valid, because what matters is the security that they find in it. (ie. The comforting feeling of control over their lives that's generated by the predictions - or, rather, that's generated by the Forer Effect.) And if these aren't the exact same thing, then they're certainly similar enough so as to negate any claim that the person who laughs has to the intellectual high-ground.
There are plenty of ways to go about making fun of people who believe ridiculous and absurd things. Let's not go inventing new ways that just discredit us.