I should state that extensive research into this issue is being conducted on a highly limited scale. :roll:

I am finding numerous sites from the lighting industry indicating that a solar temperature should produce a blue light. This is very encouraging.

Sometimes industry gets a better perspective. For instance, oil geologist, reportedly, understood crust movement before the theory had much accpetance.

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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.

What color do sun-like stars appear to be when viewed in a telescope?

General star color can be found at this site.... star colors

Your question is a good one. If "sun-like" stars look blue or yellow, then ureika. Maybe the Sloan Survey will help or Hubble pictures. However, the problems in getting "true color" are several....

1) Telescopes on Earth are hendered by bleaching caused by atmospheric effects (scattering, absorption, etc.). This causes the sun (therefore, "sun-like" stars) to look white.

2) The "color" represented by telescope imaging are not true "naked-eye" color as scientific coloring yields signifcantly more information. I suspect some images are close such as from Hubble and Cassini.

3) Like the sun, they may be too bright. Just because they are far away does not mean they will look less bright. The sun provides us with 1000 watts/sq. meter at ground level. If the Earth were twice as far away (2 a.u.), the power would be 250 w/m^2. However, it would be 1/4 in apparent size viewed from 2 a.u. This means the surface brightness will appear the same. Nevertheless, it may be that once you are far enough away so the sun is a point and not a disc, then maybe it's color is revealed.

4) To compute the color that we would see involves a great deal. The star color site has determined our sun is "pinkish peach". I am not convinced this is valid.

Now that we have SpaceShipOne, maybe they will take a strobe up with them and settle this issue. Hmmmm....I did buy a computer with Microsoft software recently...ya think they.... :roll:

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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.

Had another idea ( another s.a.d. kind)

What if we made a template in the shape of a solar irradiance curve (almost a Planck blackbody one), proportion it's size to match the eminating rays refracted from a prism, place it on the prism, allow a rectangular region of sunlight into the prism, recombine the adjusted colors via prism, and see what color emerges. 8)

The light into the prism would be sunlight itself. Sunlight is very flat across the spectrum after it has been bleached by our atmosphere. Therefore, it should be a great light source.

Here is an example of both irradiance curves (above and below the atm.) irradiance

Anyone give this a chance? 8-[

[Edit: all my ideas seem to have an oops. Oops, additional work would be needed to even the distribution of color as the template would allow more blue and green on the end (or ends depending on template design). Hopefully, the principal, hopefully, is sound.]

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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.

Let me see if I follow.

1. We take pure white light
2. Split it up into its constituent wavelengths using a prism
3. Intercept these waves with a template of the Sun's light-curve so that the light which gets past the template has the same intensity-versus-wavelength distribution as Sunlight
4. Recombine these wavelengths using a second prism to produce our own artificial Sunlight (of whatever intensity we choose)
5. See what colour we get

I don't quite get this. Surely we should start with pure white light of much less intensity than Sunlight. Isn't the fundamental problem with trying to determine the Sun's colour the fact that Sunlight is so intense it overpowers the cones, maxing them out?

Again, I don't quite follow. I thought the whole idea of the template was to ensure that more blue and green would go into the mix, since we're trying to create our own artificial Sunlight - or have I misunderstood the whole experiment?

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- Learn a lot teaching others.

Yes. The irradiance curve is a geometric representation of energy distribution as a function of wavelength. The y-axis is a derivative, so, integrating yields the total energy radiated (per unit area), which is simply the area under the curve. Pretty neat, huh. Your understanding of this is probably better than mine, but I believe I am not mistaken.

Therefore, if we have a pure flat spectrum source, we can simply cut out a template that is identical to the above-the-atmosphere irradiance curve for the sun, resize it proportionately to match the refracted spectrum from a prism to obtain the same identical amount of light for each wavelength (as the Sun radiates in space), recombine the light into a homogenous area which is reflected off of a "gray" card (which reflects all colors evenly), then observe the resulting net color.

The template could be placed onto the incident side of the second prism as this would be the spectrum's largest point.

A converging 3rd lens may be needed to help the homogenization.

The light is greatly diminished since it is enlarged as it hits the "gray" card, and we only see a very small portion of it (inverse square law, of course). We can also adjust the light intensity by simply moving the "gray" card since the light from the final lens will be converging to diverging.

However, the sun's spectrum at sea level is not perfectly flat. If you know of a "pure" white light source it would be wonderful. Nevertheless, the template can be cut to allow for the variations in it's sea level spectrum. Take the mean of this post atmosphere spectrum, then, add and subtract from the pre-atmosphere spectrum for each wavelength. This would allow sunlight to be used if no better source is available.

If, for instance, a thin horizontal beam is refracted through the prism, the template (at least the one described) would allow more blue on one side than red, for instance. Recombination with a second prism would not integrate this extra blue into the middle, so one edge of the final appearance might be blue but, probably, not the middle of the image.
A small round beam could be used, but, it will be harder to make the template and the problem would still exist.

There are alternatives for this minor problem. Instead of clipping off the edge of the red light, for instance, with the template, we could keep the sides even but place tiny obstructions evenly across the width of the beam for each respective color. However, the 3rd converging lens might eliminate the need for the extra work.

As you can see, I am trying to build from the tremendous success established by the S.A.D. experiments. :roll: :wink: But, there is still a chance I am a "few cards short of a full deck" on this idea. If it is so easy, why hasn't anyone done it (or have they?)? #-o

[Edit: Here is the location for the irradiance curves.... here

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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.

The following represents the basics of the idea....





A - Inlet slit to allow sunlight (ground level light) into SPACC.

B - White light (for simplicity, assume flat spectrum)

C - Prism 1

D - Typical dispersion

E - Template: This is a pre-atmosphere irradiance curve cut into a dark plate. The outlet light is now of the same proportions as sunlight above our atmosphere.

F - Prism 2 (to converge the light)

G - Converging light. Note that the blue light, for instance, is wider than the other colors. This presents a minor problem as all the light must be hongenized to correctly represent the Sun's "true" color.

H - Converging lens to homogenize the light. Something a little fanzier may be required. A simple convex lens will help but complete homogenization would be only at a tiny point, I think.

I - "Gray" card or something to reveal the - Suns True Color. I wonder what it is but I am hoping it is cyan or blue just to stir things up.

X - "marks the spot"!

1 - This is the above and below (sea level) irradicance plot representation. (The upper curve is the intensity of light for each color radiated by the Sun as observed in space, the lower is what we see down below after the atmosphere has "bleached" it.)

2 - If the upper curve can be used to "cut-out" light from a pure flat spectrum by the amount the sun does not emit, then the light seen will be a true representation of the color of the sun since each color will be in proportion to the suns actual color spectrum.

3- Template. The net light that passes through from a pure flat spectrum source, that is aligned in wavelength with this template, should be a true representation of the light radiated from the Sun. This light, when recombined equally into one area, will reveal the true color of our star, hopefully.

This is my thinking. If it is valid, there are some details to work out as we won't likely have a pure light source. Using existing sea-level sunlight should work if we compensate for the variations, thus producing a modified upper curve. The key point is to have the same proportions of all colors, as that of the sun, for the light that is allowed through the template.

The template will likely be placed onto the surface of Prism 2 as this would be the largest area to workwith and provides an easy "glue" point.

Well.....whata ya think? There probably is no big rush to discover the Sun's color. Afterall, it has been about 2 or 3 million years since the Sun was first discovered by man. Hmmmm, was it man's first discovery?

Regardless, wouldn't it be great if the BA could go live and announce to the world the Sun's true color debunking all the "yellow" sun nonsense. Teachers could finally give kids the proper crayon to use to color the sun and, 15 years later, they would be that much better prepared for astrophysics and, maybe, sun bathing.

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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 felt it would be best to move this to GA... here

Please post there.

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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.

In combining two ideas mentioned before on this thead, water absorbs more UV light than other frequencies. That should mean that the more water vapor the light travels through in getting to your eye, the further the color should shift away from true green toward red since UV is on the other side of the color spectrum. When the sun is high in the sky, appearing white, the light passes through the least atmosphere in reaching your eye. As the sun sinks to the horizon the light passes through more and more atmosphere and therefore water vapor. We would expect the color to shift toward red, which is what we observe.

This leaves open the issue of why we preceive white light from a green source. White is the presence of all colors in equal proportions. The equal proportions part though is probably wrong. We evolved on this planet to take advantage of the light that was available. We should see this light, whatever actual color it has, as white.

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http://members.elirion.net/~maddad
There are ten kinds of people. Those that understand binary, and those that do not.

A "green" source can be tricky. If the true color of the sun is green, it will still look white to us, as you have said. However, a green laser or led will never look white since the other colors do not exist in the light.

Not necessarily in equal proportions. If our three color cones are "maxed out", then white is the color our brains says it is. This happens when we look at the sun from space or when it is high overhead.

Other species see it different (pun time ).

White-tail deer, for instance, are dichromatic (two color cones). Univ. of Ga. and a northern univ. conducted a study I read. These deer can see extremely well in blue and, possibly, some in the UV band. Not only is their range excellent but also their sensitivity level. Of course, evolution helps them here, too. They can see all the dear hunters clearly as they sneak into their deer blinds just before dawn. The blue and violet light overhead (due to Rayleigh Scattering) is strong enough for them, but too weak for the hunters to know it.

BTW, the other color they see is yellow. So, when you see hunters saying the deer can't see their red or orange outfits and they think they are invisible - they're wrong. The deer will see them as wearing solid black against a rather bright background. [Still, the others can see them and not shoot them, hopefully]

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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.

You all seem to be doing a very good job on the experimental side of the house, but here's a couple thoughts that may (or may not) be of use:

I look at the Sun and see white.

I look away from the Sun (or any other bright, white light) and see a spot that rapidly changes colors, like my eyes can't decide what color it is.

From a design standpoint (whether by evolution or special creation or aliens-created-us or whatever), I would think that the eye would be set up so that we should be able to define "white" by "the average color of the Sun".

The fact that everything doesn't look blue seems to support this:
- Blue light is much more energetic, right?
- So our eyes don't notice it as well
- The end result is that during most of the day everything looks like it's being illuminated by white.

And it would be defined by the average color of the Sun from our perspective on Earth, since we obviously don't live in space.

As far as children painting the sun yellow, I like the idea that it's the *best* choice, but not necessarily the *correct* choice.

And I think it's probably influenced by other artwork where the Sun is yellow.

I always tried to paint the Sun red, orange and yellow because those are the colors of fire, and the Sun is fiery, right?

Although I always thought that the Sun should be blue, since it's really hot, then found out that maybe it should be white. But I've seen green flames, so temperature isn't the only determination of what color the fire is. . .

So I got confused and started making it yellow.

But I've always thought of it as white, and color it so if I can. It's just hard to denote that "this circle is the sun" without actually painting the blue sky, and a black circle looks kind of stupid.

At least those were *my* thoughts as a kid (seriously, I can remember those "fiery" thoughts as far back as 4 years old, and the "white-hot" thoughts as far back as 9 years old).

Now, it seems to me that a true test of the Sun's color would be to test how many photons from each of the basic parts of the spectrum there are (and I don't know enough about such things to know if we can even determine that, although I'm pretty sure the answer is 'yes').

But, since our eyes are biased in how they see differenct wavelengths of light, and the percieved color is formulated from some arcane equation that only our brain knows, but is somehow related to the various types of receptors and the proximity of one receptor to the other, etc., the number of photons doesn't help us determine the percieved color, just the actual color.

Anyhow, my two cents worth.

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Thanks for wading through my random thoughts of the day,
Your friendly, neighborhood Geek

I'm hopeful the answer is "yes", too.

You are correct. Color is what we see due to the no. of photons/sec, for any given wavelength, our color cones receive. The wavelength is imporant and the intensity at each wavelength is important. A plot is called spectral irradicance.

There is much you can find regarding how our eyes work. We have three color cones (often called red, green and blue cones). It is complicated because, for instance, the green cone can see yellow and some red. The green is more sensitive than red which is more sensitive than the blue.

These cones work similar to the color dots on a tv. The amount of excitation of each of a group of 3 dots (red,green and blue) will produce one of millions of different hues (colors).

White is the result of fairly even intesity for each color, I presume.

Also, if the intensity is greater than the eye can handle, white will also be a result. This will prevent the true color from being revealed. The sun's true color is not known, apparently, for this reason. Astronauts see the sun as bright white, yet, the blue and green photons are much stronger than the other colors. Down here on the surface, the intesity has been affected by our atmosphere enough to make each color intesity level about the same for all colors. Therefore, it appears white (but not when it gets near the horizon, of course).

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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.

16 Cygni A and 85 Pegasi are both G2 V, the same spectral type and luminosity class as the Sun. I bet they look white and colourless to us!

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- Learn a lot teaching others.

But what color are they when imaged through a properly color calibrated Hubble? !!!

[Added]
The color idea boils down to the difference in the two plots on the following graph..... here

[use 400nm to 700nm for vision response range.]

The intensity of colors in blue and green above our atmosphere are just too much more than what we see below our atmosphere. The lower line, the light we see down here, is fairly flat so that a white sun makes sense. But in space, the blue and green kick in hard and a net color just might be there. I just know more in the coming weeks.

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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.

Consider the following website:

http://casa.colorado.edu/~ajsh/colour/Tspectrum.html

Even though his technical capacity for black-body radiation is beyond mine, I'm sorry to say that he missed the mark on this one.

I'm a semi-pro photographer and have worked with many types of photography mediums for years, so if I may...

The peak frequency would not, by itself, determine the sun's color. Rather, it's the sum of all the frequencies over the entire spectrum (more appropriately, the medium of the area beneath the curve) which determines the sun's initial "color" as measured before it hits the eye.

But that's not quite all there is to, it...

The human eye sees some frequencies better than others. Thus, if the frequency curve were flat (same intensity across all frequencies in the visible spectrum), the color we saw as a result would tend to be closer to the frequencies in which our eyes are more sensitive.

Thus, it's not a just a matter of computing the median under the curve. First, we have to assess the impact of each frequency against our eye's proportional ability to see that frequency.

The most appropriate way to do that is to normalize both curves, making the sum of the area beneath them equal to one, then multiply them along all points, thereby obtaining a curve representing the ability of our eyes to perceive the sun's frequency curve.

Then you find the median of the area under the curve, and that's the "color" of the sun as we humans perceive it.

You know - yellow. Or actually, during noon-day, more like a very bright off-white with a slight tinge of yellow to it.

Alternatively, you can obtain a dark, chromatically neutral filter such as we use in photography, and just look at the noon-day sun for a second through that filter.

Yep - it's yellow, but not school-bus yellow. It's more like a very sun-faded manila folder yellow.

Of course the only problem with the technique I espoused above is the fact that the frequency response curves for our eye's ability to perceive colors differs from person to person. Generally speaking, however, we learn around that, so everyone knows the difference between yellow, green, and blue, for example.

I did not get the impression they were claiming peak wavelength would do so.

[quote=Rather, it's the sum of all the frequencies over the entire spectrum (more appropriately, the medium of the area beneath the curve) which determines the sun's initial "color" as measured before it hits the eye.[/quote]
So CIE stds. do not work well with blackbody spectrums?


I made a strobe (S.A.D.) and got white, but this only reduced it by 99.9% roughly. How flat is your filters transmissivity spectral curve?

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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.