Comments on: Far Out, Man: Measuring Astronomical Distances http://www.kqed.org/quest/blog/2009/07/03/far-out-man-measuring-astronomical-distances/ Science, Environment, and Nature in the SF Bay Area Sat, 21 Nov 2009 22:39:48 -0800 http://wordpress.org/?v=2.8.4 hourly 1 By: Ben Burress http://www.kqed.org/quest/blog/2009/07/03/far-out-man-measuring-astronomical-distances/comment-page-1/#comment-65129 Ben Burress Fri, 11 Sep 2009 20:37:56 +0000 http://www.kqed.org/quest/blog/?p=2949#comment-65129 Answer to question 1: Apparently it was a woodcut made by astronomer Camille Flammarion in 1888. Answer to question 2: Certainly the strength of light can be weakened as it passes through intervening material--dust, gas, etc. But even in the absense of such impeding materials, the strength of light weakens as it spreads out in space. A source of light like a star or a candle, which sends out light in all directions, weakens with distance since, the greater the distance it travels, the more space it is spread out in. Even a laser beam, whose rays are "coherent," or all traveling in the same direction and so not spreading out, weakens with distance because--well, it's not a perfect universe and even a laser beam spread out with distance. (A pencil thin laser beam fired at the Moon will have spread out to cover a few square kilometers by the time it gets there.) Answer to question 1: Apparently it was a woodcut made by astronomer Camille Flammarion in 1888.

Answer to question 2: Certainly the strength of light can be weakened as it passes through intervening material–dust, gas, etc. But even in the absense of such impeding materials, the strength of light weakens as it spreads out in space. A source of light like a star or a candle, which sends out light in all directions, weakens with distance since, the greater the distance it travels, the more space it is spread out in. Even a laser beam, whose rays are "coherent," or all traveling in the same direction and so not spreading out, weakens with distance because–well, it's not a perfect universe and even a laser beam spread out with distance. (A pencil thin laser beam fired at the Moon will have spread out to cover a few square kilometers by the time it gets there.)

]]> By: Ken Sanderson http://www.kqed.org/quest/blog/2009/07/03/far-out-man-measuring-astronomical-distances/comment-page-1/#comment-65126 Ken Sanderson Fri, 11 Sep 2009 18:04:05 +0000 http://www.kqed.org/quest/blog/?p=2949#comment-65126 Two questions: First, what is the source--and the name, if it has one--of the image of the man breaking through the celestial sphere to see what lies outside it? (My wife found it by Googling "celestial spheres," but unaccompanied by any information.) And second: how have people developed "an understanding of how the brightness of light weakens with distance"? I can guess a little: light scattering as objects get in the way, for example. But what's the full, real explanation? A very interesting blog you have. Thanks. Two questions:
First, what is the source–and the name, if it has one–of the image of the man breaking through the celestial sphere to see what lies outside it? (My wife found it by Googling "celestial spheres," but unaccompanied by any information.)

And second: how have people developed "an understanding of how the brightness of light weakens with distance"? I can guess a little: light scattering as objects get in the way, for example. But what's the full, real explanation?

A very interesting blog you have. Thanks.

]]>