After yesterday's rather depressing post about politics, today we're going to turn our eyes away from the troubled and turbulent Earth and out to the skies.
"The more we look, the more we see" sounds like a tautology, but it the realm of the sciences, it isn't. Sometimes it takes training, and careful examination of what's in front of you, even to know exactly what it is you're looking at.
This is especially true in astronomy. Consider that in only four hundred years, we've gone from:
- stars being equidistant points of light on a sphere with the Earth at the center;
- to recognizing that stars are, in fact, not all the same distance away from us, and their apparent motion comes from the combination of Earth's rotation and its circling the Sun;
- to realizing that even the nearest stars are incredibly far away;
- to discovering that the Sun is a star -- and the stars are suns -- and they're all made of more or less the same stuff;
- to the shocked understanding that galaxies are millions of light years away, are composed of billions of stars -- and there are trillions of galaxies, almost all of which are rushing away from us at breakneck speeds.
Along the way, we've discovered hundreds of different celestial objects and phenomena, some of which are positively mind-boggling, and many of which we still have yet to explain completely.
The topic comes up because of an article I read yesterday by astronomer Phil Plait. I discovered Plait a few years ago because of his excellent website Bad Astronomy (about myths and misconceptions concerning the skies). I've also read several of his books, and he's an excellent example of a scientist who is also highly skilled at bringing cutting-edge science to us interested laypeople. (I especially recommend Death from the Skies!, about which writer Daniel H. Wilson said, "Reading this book is like getting punched in the face by Carl Sagan. Frightening, yet oddly exhilarating.")
In any case, Plait's article is entitled "What Is Inside Our Galaxy's Darkest Places?", and is about dust clouds. I knew at least a little about celestial dust clouds, which are thought to be the raw materials that can eventually collapse to form stars and planets, something I touched on in a post last week. But there was a lot in the article that was new to me -- and intriguingly weird.
The dark dust clouds Plait describes are called Bok globules, after astronomer Bart Bok who studied them, and there are estimated to be millions of them in our galaxy alone. And "dark" is something of an understatement; the dust and gas they contain reduces the intensity of any light coming through them by a factor of fifteen trillion. The result is that they look like a black, starless blotch in the sky. I was immediately reminded of the Black Thing from Madeleine L'Engle's A Wrinkle in Time:
"That shadow out there." Calvin gestured. "What is it? I don't like it."
"Watch," Mrs. Whatsit commanded.
It was a shadow, nothing but a shadow. It was not even as tangible as a cloud. Was it cast by something? Or was it a thing in itself?
The sky darkened. The gold left the light and they were surrounded by blue, blue deepening until where there had been nothing but the evening sky there was now a faint pulse of a star, and then another and another and another. There were more stars than Meg had ever seen before.
"The atmosphere is so thin here," Mrs. Whatsit said, as though in answer to her unasked question, "that it does not obscure your vision as it would at home. Now look. Look straight ahead."
Meg looked. The dark shadow was still there. It had not lessened or dispersed with the coming of night. And where the shadow was, the stars were not visible.
Of course, Bok globules are just dust clouds, not the distilled essence of evil.
I hope.
But the thing that amazed me the most about these dust clouds was how little matter they actually contain, and yet how good they are at blocking light. Plait tells us that they average about a million molecules per cubic centimeter -- which seems like a lot until you find out that air at sea level contains ten trillion trillion molecules per cubic centimeter. But despite their thinness, if you put the Sun a half-light-year away from the Earth -- so, only a little more than ten percent of the distance to the nearest star --and put a typical Bok globule in between, the Sun's light would be so attenuated it wouldn't be visible to the naked eye.
Which is why I started with "the more you look, the more you see." Or -- more accurately, in this case -- the more you look, the more you realize how much we might not be seeing.
In any case, I don't want to steal any more of Plait's thunder, because you should all read his article, which is wonderful fun (and is linked above). And if you're on Bluesky, subscribe to him, because his posts are awesome.
So that's today's cool new thing I learned about the universe. Which is also valuable because it takes my mind off what's happening down here. All in all, things seem to look up when I do.
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