A shadowy question

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why06

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Yeah, Ive got to think'in one day and this strange thought hit me. <font color="yellow"> Why are shadows always unclear? <font color="white"><br /><br /><br />-Let me explain myself. Why do shadows always have a fuzzy out line to them. Theres never any clear outline. than I thought maybe its just the way the light is hitting- you know- from multiple angles. If this is so than what would a shodow look like under a laser?<br /><br /><font color="yellow">- Just a question <br /><br /><br /><br /><br /><br /><font color="black">DONT CLICK THE SITE OR ELSE? <font color="white"></font></font></font></font></font> <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>
 
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qso1

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A good question indeed.<br /><br />If you look at shadows cast by a lamp...you'll notice the closer to the light source the sharper the shadow. I don't know what the textbook explanation for this is but it has to do with the length of the shadow which is kind of comparable to focal length in a telescope. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
 
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vogon13

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For sun illumed objects, keep in mind, the sun is ~1/2 degree across. It is not a 'point source'. So all shadow generating objects will have an umbra and a penumbra.<br /><br />This makes the shadow edge 'fuzzy'.<br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>
 
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billslugg

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Light behaves exactly the same way whether it is projected or interrupted. In each case the resolution of the edge is governed by the diffraction limit. When the sharpness of the edge and the magnification approaches the minute scale of the wavelength of light (about 300 or 400 nanometers, or about half a micron, (micron is 1/1000 millimeter) then the shadow appears as a series of bands. The bands occur where the waves of light reinforce or cancel each other.<br /> <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>
 
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qso1

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Makes perfect sense to me. I should be more familiar with this subject because I can see the effects when I use shadow mapping in Lightwave 3D. Shadow mapping approximates the real properties of shadows. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
 
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search

Guest
Umbra and penumbra<br />http://en.wikipedia.org/wiki/Image:Umbra01.gif<br />http://en.wikipedia.org/wiki/Umbra<br />http://en.wikipedia.org/wiki/Penumbra<br /><br />Now off the subject but interesting:<br />http://en.wikipedia.org/wiki/Shadow<br />Faster than light<br />For objects moving at every-day speeds (much slower than the speed of light), the shadow cast by an object will move faster than the object which casts it. A cross-section of a shadow (a silhouette) is displaced by the motion of an object in front of a point source of light. The further the distance from the object blocking the light, the larger the silhouette and the greater the displacement by motion.<br />However, this simple relationship between speeds and distances becomes more complicated over vast distances for very fast moving objects due to the finite speed of light; the motion of an object may cut off the emission of light from a source to a surface, but the light that had already passed by the object will take some time before reaching the surface, and so there is some delay before the shadow on the surface reflects the updated position of the object. Thus while it is certainly possible to create shadows that move faster than light[1], this effect cannot be used to transmit information at superluminal speeds, because the motion of the shadow is being caused by the motion of the object in the past, not the present.
 
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mental_avenger

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Actually the reason shadows in Earth atmosphere have indistinct edges is because particles in the air, and the atoms of the air itself, scatter the light. The amount of scattering depends upon the composition and amount of suspended particles at that location. Also, most light sources are not coherent light, so the light they emit also spreads out and bounces off other surfaces. Shadows in space or on the Moon are sharp and clear. <div class="Discussion_UserSignature"> <p style="margin-top:0in;margin-left:0in;margin-right:0in" class="MsoNormal"><font face="Times New Roman" size="2" color="#ff0000"><strong>Our Solar System must be passing through a Non Sequitur area of space.</strong></font></p> </div>
 
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