That is when it is very strong in yellow, but is favored when it is reflected of objects such as aluminium siding. Often, when the sun is close to the horizon and appears yellow, a white object will still look white. Our brains have an automatic white balance control system to it (like nice cameras have).

I encourage anyone to try looking at a white object when the sun is yellow. White objects rarely look yellow.

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

sometimes the Sun appear blue.

When do you see it as blue?

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

When you stare at it long enough that it burns an after image on your retina. Of course then you see that blue dot everywhere you look. Or so I've heard.

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Spock Jenkins of the Vulcan Jenkins'.

The answer is that the Sun appears yellow because the sky is blue. If you don't believe this have a look at illusion 1 here:

http://www.echalk.co.uk/amusements/O...erception.html

The cross in the centre (which is grey) appears yellow when the surroundings are blue.

Nice link. The first illusion is excellent and probably does have some affect on those who claim the sun is yellow while high in the sky. A slight majority favor a yellowish-white sun based on a poll conducted here. Hmmm, maybe it's time to bump it and get more opinions.

However, notice their error in the third illusion. If you mask the two center squares, one is lighter than the other.

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

Not true. Drag a copy into photo editing software, then drag a portion of one square next to the other. They're the same, by my eyes.

How do you drag it?

I went ahead and made a physical mask, and still notice the lower square is distinctly lighter. This could be a monitor issue, although if they are the same, it shouldn't matter, I suppose. Either way, the color illusion is still valid, just not as vivid a difference if I am correct.

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

I simply used Microsoft Photo Editor and used the cut tool. This slices a rectangle that one can drag around the screen.

Due to data compression (presumably) when I expanded the screen shot 200%, each square was a blend of at least two colors, but the mixtures looked the same when placed next to one another.

That tool sounds handy. I don't have Photo Editor, though.

Here is my favorite illusion.

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

Excellent! There were many I had not seen before. The two triangles took me a minute.

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

couldnt it be just the right combination of an optical phenomena where one sees yellow whent the surroundings are blue, and also the particular wavelength that the sun emits colour in?

I suspect the surrounding blue can be a factor. Also, it may be the outer edge of the sun would actually appear yellow if isolated from all other light. This is because only the upper atmosphere of the limb (outer edge) is all we can see and it the upper atmosphere of the sun is cooler. Thus, we will receive more greens, yellows, and reds than in we see in the central disk regions. The temperature difference we see at the limb is around 5000K vs. the central region of 6390K.

However, the worlds largest solar telescope (McMath-Pierce at Kitt Peak) reveals the disk to be all white. But, I need to be sure they use no filter. Another possibility is the fact they are over a mile above sea level which reduces the loss of blues due to atmospheric extinctions.

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

I'm not willing to concede the sun is yellow. I challenge my students to look at it. It's white!

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Michael Huster
Simpson University
Redding, CA

Welcome to BAUT, Michael. You are sounding like a future heliochromologist already!


There is a poll regarding how others see the sun's color which you might enjoy. Please place your vote, too.

Here is a post that includes a picture of an unfiltered solar projection taken at the world's largest solar telescope: the McMath-Pierce at Kitt Peak. It sure looks white to me.

Serious Warning: The rods and cones within the eye are easily damaged by excessive direct sunlight. Using a solar projection via a pinholed sheet is the safest.

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

at 15, I'm pretty young to be posting a comment, but if the sun looks white when we stare up at it mid-day, and then looks yellow in a sunset, then I believe the question really is, what is different? We know the sun didn't just change colors, and we know that the atmosphere is the same everywhere. So why is it different? I'm a little confused.

There's no question like a good question, and you are one.

Welcome to the board.

You are on the right path in finding the answer. Think a little more on what is really different. Perhaps imagining the Earth at a distance where you can see land, atmosphere, and sunlight going to an observer when the sun is overhead and when it is on the horizon for the same observer will help you see better. Is there anything you see different?

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

I guess I notice that there is more atmosphere that the observer is looking through when it's on the horizon, then when it's strait up. your eye path to the sun encounters less atmosphere, therefore it's a possibility that it has something to do with how much atmosphere is in the way of the sun. Hmm. that's a good point.

The atmosphere is filled with minute particles called aerosols. These particles are of about the same size as the wavelength of visible light and scatter light at the short 'blue' wavelengths' a bit better than they do the longer-wavelength 'red' light. This means that as we look towards the sunset on the horizon, our path through the atmosphere intercepts lots of this aerosol material which preferentially scatters the blue component of the incoming sunlight out of our line of sight. The light is then reddened. As we look up towards the zenith over head, we are not seeing the sunlight coming directly from the Sun, but are seeing the light scattered by the aerosols at large angles to the line between the aerosol particle and the Sun. This light is blue because it contains little if any red light which is not scattered as well by the aerosols. The rate at which blue replaces red light as you go from the horizon to the zenith at sunset and sunrise can be used to determine the optical properties of the aerosols and their size distribution. I think that basically sums it up. but if there's something wrong, please let me know. also, I need help with finding out how to post a new thread. could somebody please help?