Fidgety stars?

Piggy-backing off my earlier post about “star streaks,” I’d like to add the following.

INSCITIA:

Given that stars appear immobile due to their tremendous distance relative to us, why do they still appear to shimmer and twinkle and twitch?

This question bothered me the night I was up in Da Keng.  I was surprised to (re)discover how animated the stars looked, thinking that one of them was as close to a UFO as I'd ever seen.  Happily, I was able to get a responsum to this inscitia just by googling.  (Which, of course, raises the question how viable this whole ignorance blog is, since I may be able to find responda to all my inscitia just with enough googling.  Even so, I like the idea of admitting on ScIn when I’m ignorant.  This blog is, as I say, as much a discipline of learning as a forum for cultivating humility.  Plus, I really would love to hear from knowledgeable readers, thus bringing collective wisdom to me in a personal, interactive way.)

RESPONSUM:

[A]tmospheric turbulence produces continual small changes in the optical properties of the air between the star and our eyes. The light from the star is refracted slightly, and the stellar image dances around on our retina. … Astronomers use the term "seeing" to describe the effects of atmospheric turbulence. The circle over which a star's light is spread is called the seeing disk. On a good night at the best observing site, the maximum amount of deflection produced by the atmosphere is slightly less than 1 second of arc. The seeing disk of a star is only a small fraction of an arc second. The point-like image of a star is seen as scintillating. (c/o the Singapore Science Center)  

So, there you have it.  The “UFO” twitching I saw New Year’s eve in Da Keng was atmospheric, not astronomic (a fact which I suspected at the time, since the most dramatic twitching came when clouds passed over and past stars).  Ironically, this atmospheric “interference” is actually a key part of our enjoyment of stargazing.  if we saw stars “as they really were,” without any “seeing” (atmospheric disturbance), we might just find them boring.  Twitching, disturbed real stars are and always will be much more enthralling than perfectly observable, static glow-in-the-dark sticker stars.  

Along the same lines, I recently read how the coffee-table-book photos we have of our galaxy and of other astronomical entities get nearly all their beauty and splendor from photo filters, digital touch-ups and, most important, prolonged shutter exposure.  The pictures we see of the Milky Way as a lush, swirling mass of stars and planets is actually due to immense light saturation, basically galactic photographic steroids. If we saw a true “snapshot” of the Milky Way, or of any part of space in general, we’d see an unimpressive huge black matte peppered very lightly with stars and asteroids.  Regardless how dramatically PBS animates it for public education, emptiness and darkness, not fullness and brightness, are the chief attributes of space.  

An irony for me was that I read about this in a book defending the likelihood, if not biological necessity, of extra-terrestrial life.  I find this ironic, incongruous, because a key premise in the SETI movement is that, even if we leave aside intrusive comic-book “grays” and “Martian men,” virus- or bacteria-laden space debris flitting from plane to planet, suffice to pollinate the whole cosmos with low-level life.  Oh, really?  The fact is, as this book pointed out, if you sent even a large rocket through space, it would in all likelihood travel “billions and billions” of light years without a single collision.  Presumably, SETI’s hypothetical life-rocks have better odds of touching down.