Critiquing an Astronomical Meme

January 4th, 2013

Mistakes are just teaching opportunities!  :)

I recently saw this being passed around facebook:

iflsstarsI don’t know the original source, but the most recent was I fucking love science, who often has great posts.  So what’s wrong about this one?

Almost all the stars we see in the sky are relatively local, astronomically speaking.  Tens, hundreds, or a few thousand light-years away at most.  The Milky Way itself is only on the order of a hundred thousand light years across, and due to the gas and dust in our galaxy, and the fact that stars aren’t all that bright given this huge distance, we just don’t see a very big part of our own galaxy without the aid of telescopes.  Only those with excellent eyesight at dark locations can even make out the fuzzy light from external galaxies, so the discussion is really about the few thousand easily visible stars in the sky.

Now, the lifetimes of stars vary tremendously, from a few million years for the most massive and luminous stars (which are exceedingly rare), to perhaps a trillion years for the ubiquitous M stars also known as red dwarfs.  Our own sun has been burning for five billion years and will be around for another five billion or so.

So the argument put forth above is that “many” of the starts in the sky (sounds like anything from hundreds to thousands to me, but more than a few or a handful) are within a few thousand years of their end, even though a thousand years is a tiny fraction of a stellar lifetime for all but a handful of the most massive stars in our sky — of which they are only a few, since they’re rare.  Now, there well may be a few (not many!) that are already dead.  Betelguese, the left shoulder of Orion, is one of them.  Eta Carinae is another.

Let me make an analogy.  Let’s say we watch a day of TV, all TV shows from the past few years (some new, some repeats).  You say, “Good friends are like stars — celebrities on TV.  They’re always there.”  Then your dorky know-it-all friend says that most of the shows were not live but recorded a few years ago, so many of the people on those shows are already dead.  That’s BS, obviously, because a year or two ago is a short time compared to the typical lifetime of humans, and terminally ill/extremely aged actors are rarely seen on popular entertainment.  Sure, a few actors or other TV personalities might have died, sure it happens, but saying “many” with certainty would be a bet few should take willingly.  (Obviously things would be different if you were watching Turner Classic Movies or another TV channel featuring old shows from a bygone era — the equivalent to pointing your telescope at a galaxy in a distant part of the universe billions of light years away.)

And for my money, stars become even more romantic the more you learn about them.


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