PDA

View Full Version : Yellow Sun



Hat Monster
2002-Mar-22, 09:23 AM
Says in the book (ARRIVED TODAY! WOOHOO!!) that you can't work out why the Sun appears yellow, Phil.

I think I've got it.

The blue photons are scattered everywhere. Fine, great.
The red are pretty much coming from the direction of the sun.
What about the yellow and orange? They'll be scattered not as much as the blue, but more than the red. They'll appear to come from *near* the sun, giving the area around the Sun a YELLOW look. Squint and look up. See for yourself.
Green also comes into it. Mix green light with blue light, our eyes see yellow, so the slightly scattered green will enhance the effect.

Simon
2002-Mar-22, 12:22 PM
On 2002-03-22 04:23, Hat Monster wrote:
Green also comes into it. Mix green light with blue light, our eyes see yellow, so the slightly scattered green will enhance the effect.


I'm not strong on optics, but I doubt blue+green would make yellow. With computer graphics, at least, green and blue together make a light, sky-blue.

Hat Monster
2002-Mar-22, 02:08 PM
Red and green make yellow. My bad. But this just reinforces my statement further. Remove blue from the areas around the sun, you're left with yellow.
See:
<font color="#FFff00">Yellow</font>
That colour was #FFFF00. This is arranged as RRGGBB, for red, green and blue. Your monitor can emit red, green or blue light and no other. Look closely at the screen, maybe using a hand lens. Red, green and blue dots. Look at the text above, the yellow. Notice only the red and green are turned on? That's because the notation (#RRGGBB) is in hexadecimal, numbers from 0 to F with A coming after 9. FF is 255, the highest possible. So the #FFFF00 tells your monitor to display full green and full red. You see yellow.
Physics is under no obligation to be easy to understand.

<font size=-1>[ This Message was edited by: Hat Monster on 2002-03-22 09:10 ]</font>

<font size=-1>[ This Message was edited by: Hat Monster on 2002-03-22 09:10 ]</font>

GrapesOfWrath
2002-Mar-22, 02:20 PM
On 2002-03-22 09:08, Hat Monster wrote:
Red and green make yellow. My bad. But this just reinforces my statement further. Remove blue from the areas around the sun, you're left with yellow.
Actually, the BA does discuss that very thing, on pages 45-46, but he says that the amount of blue removed is not enough to account for the effect. He doesn't provide actual numbers about how much is removed, but he does address the issue.

I'm not sure he's right about that, though. One of his examples is the color of a white sheet of paper--it is reflecting sunlight, so he claims that sunlight is white. But it is also reflecting the blue, so it is effectively recombining the light with the blue.

We're going to have to dig out the actual numbers, to see what's up.

SeanF
2002-Mar-22, 02:32 PM
On 2002-03-22 09:08, Hat Monster wrote:

Look closely at the screen, maybe using a hand lens.



Okay, did any of the other regulars nearly have a panic attack when they read this?

Nothing against you or your post, Hat Monster -- a previous poster a while ago suggested using a magnifying glass on a computer monitor for completely different (and wildly inappropriate) reasons . . .

And by the way, your theory does make a certain sense to me. /phpBB/images/smiles/icon_smile.gif

Roy Batty
2002-Mar-22, 04:31 PM
-- a previous poster a while ago suggested using a magnifying glass on a computer monitor for completely different (and wildly inappropriate) reasons . . .


Ieee! just remember, nameless, always nameless. Pi.. /phpBB/images/smiles/icon_smile.gif

Hat Monster
2002-Mar-23, 12:02 AM
Hey, I used to be a regular too, back when the BABB was still WWWBoard.

Simon
2002-Mar-23, 12:00 PM
Okay, I've just gotten the book (as in, it arrived half an hour ago) and I agree with GOW: We should dig up some numbers on this! /phpBB/images/smiles/icon_wink.gif