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Author Topic: Sky/Cloud Colors  (Read 2884 times)

dennis

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on: December 31, 2010, 11:56:19 PM

Here is a chart I made several years ago to help my students understand the colors in the sky and why colors change at different times of the day.


Very briefly, and without going into the technial side of things, light rays have to travel through the layers of our earth's atmosphere and in doing so they are scattered to different degrees according to the frequency of the color.

Light Scatter

Let's start from noon time. Here the light rays have the shortest distance to travel through the troposphere (distance A) The sun is at it's brightest (strongest) and the blue rays practically bleach out all the other color rays coming through the atmosphere and that is why the clouds look white in the middle of the day (not so much the reflected rays off solid object on the earth).

As the sun moves away from you towards the horizon the rays have to travel through a longer and longer path as the sun begins to set. You can see these distances on the chart - B,C,D and E. As the blue frequency is the most vunerable to being bent by dust particles, polution, heat rays, moisture, etc, they are the first to start to disappear as the path gets longer through the atmosphere. The other colors are also getting scattered, but less and less so as they approach the red frequency. That is why we mostly see the red color just before and while the sun is settling down for the night!

Obviously the right side of the chart is mirrored on the left.

Reflected Light off Clouds

Next we see that the rays at noon are so strong and bright that the reflected light off the clouds causes our pupils to contract and so we see only contrasts and not so much the color in the clouds. As the sun sets our pupils begin to dilate and we begin to see the colors much better. White and any other light color will easily reflect other colours around it.

If you want to take photographs for painting purposes the worst time to take them is between 10 in the morning and 3 in the afternoon. This is a general statement and you will have to modify it to suit the country and area you live in. Hope you get the picture (very punny!)

Cloud Colors
From the chart you can now see why the clouds appear white in the middle of the day and the clouds colors start becoming a  light yellowish color to a darker yellow, moving through to yellow-orange, etc, right through to the dark red at sunset or sunrise.

TIP Use either naples yellow and/or yellow ochre for yellow in the clouds - they are less prone to becoming green when blended into the blue.
Also when you have a yellow glow on the horizon buffer a very light section of orange on the edge of the yellow before blending into the blue of the sky color. This prevents a green halo where the yellow and the blue meet.

Study the chart and hope this will be of help to you.
You are what you THINK about - Napoleon Hill


Kelley

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Reply #1 on: January 01, 2011, 01:17:43 AM
I don't know if it is true everywhere, but I noticed that at the opposite side of the sunset the sky is violet, blue and all the way to red as you turn 180 degrees to face then sun.   I've taken pictures where some objects are silhouetted against the Sun. Then in the opposite direction objects appear to pick up the "colour" or refracted light of the sky.
Kelley


dennis

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Reply #2 on: January 01, 2011, 02:51:51 AM
Hi Kelley
New Years day here at the moment so Happy New Year to you!
Here is a quick explanation of your observation. Will replace with  a proper illustration later.



What you are observing is the color spectrum in action. As you turn from looking at the late evening sun and  you turn 108 deg you are actually following the spectrum.
You are what you THINK about - Napoleon Hill


Val

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Reply #3 on: January 01, 2011, 03:43:12 AM
Now this is interesting. That chart will come in very handy. Thanks again Dennis.  O0
Cheers, Val

�Creativity is allowing yourselves to make mistakes. Work on knowing which ones to keep!�

- Alvaro Castagnet


Kelley

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Reply #4 on: January 02, 2011, 09:21:25 PM
That is precisely right Dennis.  With what is in the atmosphere it's almost as if the entire sky from horizon to horizon is a rainbow at sunset.  Most noticeable when there are clouds.  I've been trying to study the evening sky to learn the effects but I just to watching in amazement that I forget to document anything.
Kelley


nolan

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Reply #5 on: January 02, 2011, 10:31:23 PM
I've been trying to study the evening sky to learn the effects but I just to watching in amazement that I forget to document anything.


Know the feeling  ;D

There is also a similar explanation on why is the sky blue in another post.


Kelley

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Reply #6 on: January 03, 2011, 01:20:23 AM
 O0
Kelley


Val

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Reply #7 on: January 04, 2011, 09:29:23 AM
Kelley...I took note of your comment about documenting. Decided I'd do just that via photos. You're absolutely right  ??? get so caught up watching...missed a few photos in the middle!  :2funny: Not much of a story without the middle!  ;D Nice thing is...if you don't get it right the first time...you get to do it again tomorrow!  :clap:
Cheers, Val

�Creativity is allowing yourselves to make mistakes. Work on knowing which ones to keep!�

- Alvaro Castagnet


nolan

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Reply #8 on: January 04, 2011, 10:51:53 AM
saw the most amazing sunset tonight, but was at the beach with no camera  :'(
Maybe we should have a sunset competition to see who can take the best sunset photo this week, then we paint the winning photo next week. Then we get to compare the different styles / interpretations?


Val

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Reply #9 on: January 04, 2011, 11:58:14 AM
That sounds like a fun idea!  :clap: Where shall we post the photos? Choice of mediums?  :confused:
 :painting: :painting: :painting:
Cheers, Val

�Creativity is allowing yourselves to make mistakes. Work on knowing which ones to keep!�

- Alvaro Castagnet


nolan

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Reply #10 on: January 04, 2011, 12:53:00 PM
Here is the thread I have created for the painting challenge

You can paint in any medium and style O0


 

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