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Paddy O'Flanigan
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Join Date: Feb 2005
Posts: 255
Good Answers: 2

Parallel Sun Light?

10/10/2006 8:48 AM

Last month I asked a question about the equinox and how sunset can occur directly in the west in all locations on earth. The consensus explanation was that for all intents and purposes, the light from the sun is received in parallel "rays" from the sun and therefore the sun appears due west from all points on earth on the equinoxes.

This morning, driving east into work, light from the sun was filtering through the clouds in a very pretty fan shaped pattern, far from parallel. Can someone help me understand how the sunlight we receive can be parallel and fan-shaped at the same time?
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Pathfinder Tags: equinox sun beam sun rise sun's rays sunlight
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Jorrie
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Engineering Fields - Aerospace Engineering - Retired South Africa - Member - The Rainbow-nation Engineering Fields - Engineering Physics - Relativity & Cosmology Popular Science - Cosmology - The Big Picture!

Join Date: May 2006
Location: Pretoria, South Africa
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#1

Re: Parallel Sun Light?

10/10/2006 1:08 PM

Yep, those "fan shaped patterns" can be really pretty! I think they come from a combination of refraction of light by water droplets and some scattering due to collisions with water/dust particles. Anyone with more info on those?

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bhankiii
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Engineering Fields - Electrical Engineering - New Member

Join Date: Sep 2006
Location: El Lago, Texas, USA
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#2
In reply to #1

Re: Parallel Sun Light?

10/10/2006 1:58 PM

It's simply the geometry of perspective, isn't it? The same reason that parallel train rails seem to converge into a point, only in reverse.
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user-deleted-13
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Join Date: Sep 2006
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#4
In reply to #2

Re: Parallel Sun Light?

10/11/2006 4:03 AM

Bingo! --Europium
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rcapper
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Join Date: Dec 2005
Location: Etats Unis
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#3

Re: Parallel Sun Light?

10/11/2006 12:48 AM

Sounds like a pin-hole lens. Maybe a little bigger than a pin-hole but it's a relative thing. It never occured to me about the west thing but I guess when the "point source" is bigger than the target you have that kind of thing.

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