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.

An added bonus?

I am currently revising an FCA article. I wanted to write "As an added bonus..." but then backtracked to write the leaner, seemingly non-redundant "As a bonus...".

INSCITIA:

Does is it make any sense to say "an added bonus"? Isn't the very meaning of "bonus" something that is "added"? Does an "added bonus" amount to a "bonus bonus"?

COGITATIO:

I know (I think) that in Latin "bonus" simply means "a good." But I think in modern English, "bonus" carries the idea of an extra, even gratuitous, good. As such, it is redundant to speak of an "added bonus." An unadorned bonus is bonus enough, no?

RESPONSUM:

Star streaks?

I was in the mountains last night for New Year's. Finally above Taiwan's smogline, I was actually able to see -- stars! Seeing them again for the first time, I was amazed at how "fidgety" they all seemed to be. No matter how hard I stared at them, and in fact, the harder I stared at them, they seemed to twitch and in some cases even change position. ("No wonder there are so many UFO sightings," I mumbled.) Thinking with such wonder about starlight, I recalled that the starlight we see is in fact old news: the light currently being emitted by the stars has not yet reached earth from so far away, so when we look up, we only see stars' old, well traveled photons.

INSCITIA:

If the earth is moving and if starlight reaches us in a stream of photons, why don't we see stars as streaks across the sky? Indeed, isn't the North Star so very bright just because earth 's axis moves in line with it, and therefore more photons from the star can hit us directly, without any terrestrial shift?

Imagine a man spraying a hose to the side while running: the water bends back as he runs forward. How or why doesn't the same go for starlight? Or imagine taking a photo of moving cars at night, with a long shutter exposure: as the photons collide into the camera's retina, the moving lights form streaks in the final photo. In both cases, the dynamics are reversed (the stars spray and are stationary, while the earth gets sprayed [with photons] and is in motion), but I think the analogies holds.

COGITATIO:

I assume the answer has to do with the immense distances of the stars from earth, and that from that far out starlight somehow "equalizes" around its originating point, so that we see the mean amount of light and recognize it as a star. In other words, the stars we see are like visual "statistical averages" of photons, and they appear to contract into one star. Since the only thing consitstently producing light is the star, it is the only thing that will reach our eye on a "statistically mean" frequency. Any twitching by the stars, then, would just be the batches of photons outside the star's statistically mean core.

RESPONSUM PRIMUM:

As of 4 December 2006, my co-workers quickly disabused me of my ignorance on this one. "It's distance versus speed, dude," they said. They reminded me that if we leave a camera shutter open a while at night, we will indeed see streaks. I am supposed to understand that because the stars are so very far away, we simply can't perceive their motion. It's like sitting on a train watching the far mountains "stand still" while the nearby grass, fences, ground, etc all zoom by.

This explanation is obvious and simple. Even so, I can't shake my sense of curiosity - which I'll say is so inchoate as to amount to ignorance - as to WHY such a phenomenon occurs. It still seems there must be some kind of perceivable alteration of the stars based on our terrestrial motion, much as the sun changes appearance just in relation to our orbit of it. "You can lead a fool to wisdom..." I suppose? I accept the explanation, but something elemental still tantalizes and eludes me at a deeper level about this phenomenon. Hmmm...

RESPONSUM SECUNDUM, care of "the other e.b.":

We can see the stars move due to terrestrial motion, paralax, dude.

Some practical explanation. Close an eye (any eye) and raise your thum to a fixed point on a far wall... now switch eyes, your thumb appears to have moved relative to the fixed point, right? Yeah baby, paralax.

And if you think about it this would work for "closer" objects as the earth moves around the sun. For instance durring summer a certain relatively close star would apper distance x away from a "fixed" star (one whose distance is so astronimically far that it appears unmoving even relative to our solar orbit). However, as the year progresses to winter the earth moves around to the other end of its orbit (like "switching eyes" in the previous example) and we now see the "close" star from a slightly different angle and it now looks as though it has traveled to a distance y from it's "unmoving" neighbor.

This only works for stars that are on the order of "astronomical units" away from us (one astronumical unit (au) is the distance from the earth to the sun, or thereabouts [using a base line of "1 AU" made some of the math easier given that, at the time, astronomers had no idea what the true distance was])

So, if we know the distance the earth has moved (roughly 2 au's), and we can see how much the "close" star has "moved" agains the relatively fixed background we can then extrapolate a distance using simple geometry (the earth's orbit is a base of a right triangle and the angle can be deduced from the amount the "close" star travels, apply the pathagorian theorem and there you have it).

pax

Volo scandeo inscitia mea!

"I want to mount my ignorance!"

The idea of this blog is to voice any and all areas of my ignorance. Astronomy, history, languages, biology, politics, theology, etc. -- anything I recognize as a dark spot in my mind, I'll post here.

Why?

Two reasons.

First, admitting and then broadcasting my ignorance cultivates humility; and humility is key to spiritual growth. I, like many people, glibly devote so much of my blogging to announcing what I think, presumably because it's what I think I know. How sobering it is to devote whole blog to what I don't know! If I were really alert and honest, this blog should quickly swell to tenfold the size of my other writings. Hence the title: mounting ignorance.

Second, while I must face my vast ignorance, I won't wallow in it. By posting quandries here, I am genuinely seeking knowledge. Hence the title: mounting ignorance [to overcome it].

The format of Scandendum Inscitia (ScIn, "skin") is as follows: I'll provide a context for my ignorance and then lay down my ignorant query (INSCITIA). Then I may or may not offer some thoughts about how to resolve my ignorance (COGITATIO). Either way, the post will end with space for readers, or my own subsequent learning, to resolve my inscitia (RESPONSUM). (I'll transplant the responsa into the post from emails or comments readers offer.) Hence, this blog in no small way depends on readers willing and able to help me mount my ignorance. May my inscitia yield unto God's sapientia.

Finally, I resist the common stereotype of the Middle Ages as a dark and mindless, as a dead and lifeless, age. The longer one studies that era, the more one is impressed, even stunned, by the medievals' voracious desire for learning. Plus, if you read St. Anselm or other medieval giants, you can't miss their humility. While they may pontificate and explicate about the highest mysteries, they all the while make it clear they do so as weak and ignorant mortals walking by the humble light of fides quaerens intellectum (faith seeking understanding). Given my sympathies for the Middle Ages, and given that age's utterly Latin composition, I hope to use Latin frequently here at ScIn in a true medieval, voracious and humble pursuit of sapientia. Besides, using Latin here will help me maintain and regain my middle-school Latin.

INSCITIA:

Have I left anything out?

RESPONSUM:

INSCITIA:

Where is my Latin wrong?

RESPONSUM: