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Crepuscular Rays

11/14/2010 11:16 PM

Crepuscular is a word with a catchy sound, and it is easy to work into any conversation about dusk or dawn... but it is rarely heard. If you search for it here on CR4 you will find that it shows up a couple times, but not in association with rays, which is the topic of this post. Plenty of animals are crepuscular, meaning that they are active around twilight (dawn or dusk). On Halloween, you could tell your kid that it's too crepuscular to start trick-or-treating... but I bet you've not used the term for that purpose. Perhaps the reason the word is seldom heard is that its sound seems so different from the concept: crepuscular sounds like it should mean ugly and crusty, with a little pus thrown in for good measure.

Crepuscular rays are these things that you can see near sundown and sunset:

When these emanate from behind clouds at the correct angles, they are good for measuring the sun's distance from earth. In the picture below, we can see that the sun is really 4.5 miles above the earth's surface if we do the simple triangulation required, using the distance between surface points where the rays hit the earth, and some trig.

Those scientific nutcase types will try to tell you (probably already have) that the sun's rays are essentially parallel as they reach earth. This is of course not true, cuz you can see the the rays in these photos, and they are clearly not parallel.

Those who want to control your mind say that these rays are really parallel, but look as if they converge, for the same reason that railroad tracks appear to converge. If you give the issue some thought, you might agree with such types... but my advice is to avoid such thought because it can lead to the conclusion that the sun might not orbit the earth, and that is is actually far, far away.

In the middle of the picture above, you can pick out a nearly vertical ray that is directly below the sun. The party poopers will tell you that this ray is not really vertical, but that it is instead nearly horizontal as it comes toward you, but appears vertical. Oh come now!

If you believed the poopers, then the photo below would look like a contrail at, say, 35000 feet. If you believe the alternative, "earth is just a few miles beneath the sun" reasoning, then this contrail could look like a missile launch. Several news organizations, especially CBS, subscribe to the latter line of reasoning, and reported the contrail as a missile launch. Amazingly, they came up with an approximate distance off shore where the "launch" occurred... and even found an expert witness to say that the launch might be a show of American might while Obama was in China. (Believing this would require several large leaps of logic. One could ask, if there is some lunatic in control who thinks that we need to demonstrate military might to China, then why not just blow up something big over there... how is a launch over here, which we already do routinely, going to intimidate the Chinese... as if we would want to intimidate our owners, in the first place.)

Contrails and rocket launches can look somewhat similar when seen as static 2d photo representations.

But seen in real life, with the benefit of human 3D perception, it doesn't take long for a reasonably thoughtful and responsible person to say: "Hmmm... can't be a rocket launch because it's not growing at anywhere remotely close to the right rate for that... and it sure looks like the "launch point" is way out in the distance... a jet contrail seems a much better fit." Those few seconds of reflection might have prompted a web search, where one could find images of a contrail from last New Year's eve that looked nearly identical and caused a stir, too.

But where's the story in that? Far more fun, and better viewership, if you can make something dramatic, create the hype, and then blame the hype on others. CBS said the launch "lit up the sky." It did not, because the thing lighting up the sky during a sunset is the sun... and missile launches do not produce incredibly long bright trails: the bright spot is just behind the missile. If the sky were lit up by a launch, others would have reported sudden brightening and subsequent sudden dimming of the sky. Does anyone here really think that the bright cloud in the photo above is being lit up by the contrail?

Why was the edited video cut before the point where the camera shows the airplane out ahead of the plume?

Things were hardly hysteric at CR4, but you can see how irresponsible reporting can (in addition to being insulting to the military, the FAA, homeland security, etc) fuel hysteria and conspiracy theories.

Search google images (and wikipedia for info) for crepuscular and anti-crepuscular rays -- lots of beautiful shots. While looking for crepuscular ray photos, I happened upon this collection of various photos, which are pretty stunning. Enjoy.

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#1

Re: Crepuscular Rays

11/15/2010 12:46 AM

Now I'm just waiting to hear about Newton's corpuscular theory of light!

[Sorry, couldn't resist.]

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#2

Re: Crepuscular Rays

11/15/2010 7:36 AM

Not this again.

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#4
In reply to #2

Re: Crepuscular Rays

11/16/2010 12:25 AM

Fear not. I posted mainly to share the link to the photo collection I happened to find when looking for crepuscular ray photos (which I was interested in mainly because of a dramatic sunset last night which I discussed with my daughter re the physics and perspective, etc.). I've been intrigued by crepuscular rays. While we accept the convergence of railroad tracks without thinking much about it (so the tracks appear parallel) the crepuscular rays really look like they cannot be parallel -- you can imagine early civilizations thinking that the sun was close enough to melt your wings if you flew too close.

Secondarily, I took the opportunity to rant about CBS. I am of the about the same mind as redfred who wrote, in the "missile" thread: Now I hope somebody sues them or arrests somebody for inciting a riot. Shouting FIRE in a crowded theater is not free speech, its a malicious crime. Granted, most reporters are clueless regarding this sort of stuff, but that's why there are fact checkers, etc. No one will be arrested, and no suit is likely to be filed, but this stuff is irksome. Reminds me of a TV station in Tampa FL that gave a glowing report re an HHO unit that was advertised on the TV station's website. They did an obscenely poor job of "testing" the unit, and the HHO promoter sold many units as a result. The FCC should yank licenses of stations that do not operate in support of the public good.

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#3

Re: Crepuscular Rays

11/15/2010 3:42 PM

This is of course not true, cuz you can see the the rays in these photos, and they are clearly not parallel.

I completely agree with you. This is why I intend to prove what you are saying. I'm going to take a picture of the rail road lines, on a stretch of, say, one mile. We all are going to see that they are converging into a point not very far from the observation point.....R..R...or something like that, dear Bumble.

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#5

Re: Crepuscular Rays

11/16/2010 12:58 PM

Thank you for the download of these beautiful photos from that collection - I spent at least half an hour taking in the intricate details of these intuitively experienced visions of what the various artists are appreciative of, and are willing to share, and which few, if not most of us are unaware of, until brought to our immediate and most times, brief span of attention/concienceness. - It truly is a beautiful world - Loupy

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#7
In reply to #5

Re: Crepuscular Rays

11/17/2010 11:09 AM

It truly is a beautiful world

Indeed. Thanks for your comment. Photographs can allow us to see things that would otherwise be missed. Sometimes this is more literally the case (as in the wings of a swan frozen in time) and an other times the photograph draws our attention and enables us to focus on an element of nature that might otherwise have blended into the noise of daily existence.

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#6

Re: Crepuscular Rays

11/16/2010 3:51 PM

It seems like it would have been fairy easy for someone Vandenburg AFB or at LAX to not only rule out the possibility of the streak being a missle, but also expediently identify the actual flight of any plane on a flight plan in the area. .. why only after considerable debate/delberation was it claimed that it was 'probably' a plane. is this the work of the inept? The corrupt? The sensationalists? . . .. . . . ... .. . .bbb.

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