APOD: All the Colors of the Sun (2013 Oct 02)

Comments and questions about the APOD on the main view screen.
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APOD: All the Colors of the Sun (2013 Oct 02)

Post by APOD Robot » Wed Oct 02, 2013 3:59 am

Image All the Colors of the Sun

Explanation: It is still not known why the Sun's light is missing some colors. Here are all the visible colors of the Sun, produced by passing the Sun's light through a prism-like device. The spectrum was created at the McMath-Pierce Solar Observatory and shows, first off, that although our white-appearing Sun emits light of nearly every color, it does indeed appear brightest in yellow-green light. The dark patches in the above spectrum arise from gas at or above the Sun's surface absorbing sunlight emitted below. Since different types of gas absorb different colors of light, it is possible to determine what gasses compose the Sun. Helium, for example, was first discovered in 1870 on a solar spectrum and only later found here on Earth. Today, the majority of spectral absorption lines have been identified - but not all.

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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by MargaritaMc » Wed Oct 02, 2013 7:10 am

http://asterisk.apod.com/library/APOD/A ... 31002.html

A friend passed me the above link that gets to today's Apod. When I followed the link given at

http://asterisk.apod.com/viewtopic.php?f=9&t=32210
( which is http://asterisk.apod.com/library/APOD/A ... irror.html)
there were no Apods more recent than 2010.

Today's Apod was the image that first helped me to realise how enormously complex is the subject of the spectra of stars.

A quotation from text link to:
http://www.noao.edu/image_gallery/html/im0600.html
"Each of the 50 slices covers 60 angstroms, for a complete spectrum across the visual range from 4000 to 7000 angstroms."

Fascinating!
Margarita
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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by Nitpicker » Wed Oct 02, 2013 7:27 am

MargaritaMc wrote:there were no Apods more recent than 2010
Looks like a typo ... "2010" should be "2013".

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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by MargaritaMc » Wed Oct 02, 2013 7:42 am

Nitpicker wrote:
MargaritaMc wrote:there were no Apods more recent than 2010
Looks like a typo ... "2010" should be "2013".
Duh! :roll: It didn't occur to me to click on them at LOOK!
THANKS!
"In those rare moments of total quiet with a dark sky, I again feel the awe that struck me as a child. The feeling is utterly overwhelming as my mind races out across the stars. I feel peaceful and serene."
&mdash; Dr Debra M. Elmegreen, Fellow of the AAAS

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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by Ann » Wed Oct 02, 2013 8:33 am

The truly great thing about this picture is that it shows us all(?) or at least definitely most of the Sun's spectral lines. (There might just possibly be a few lines there which are so weak that they don't show up clearly in this picture.)

Spectral lines are of course incredibly informative when astronomers try to learn the nature of stars. Indeed, spectral lines tell us quite a lot about the dominant populations of galaxies, too. And obviously they tell us about redshift too, precisely because the spectral lines will be shifted to the red in the light from almost all galaxies.

I'm going to offer a nitpick, however, and say that this picturre does not, in fact, show us all the colors of the Sun. The color violet is missing. The violet color can clearly be seen in this picture of a rainbow, so presumably violet is a real color of the Sun. Another color which is there in today's APOD, but which gets rather short shrift, is orange.

The colors of the Sun, judging from today's APOD, are sharply red, green and blue, with a few "intermediate colors". I would guess that the reason for this three-color aspect of the Sun is that it was photographed through red, green and blue filters.

Ann
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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by geckzilla » Wed Oct 02, 2013 1:00 pm

MargaritaMc wrote:
Nitpicker wrote:
MargaritaMc wrote:there were no Apods more recent than 2010
Looks like a typo ... "2010" should be "2013".
Duh! :roll: It didn't occur to me to click on them at LOOK!
THANKS!
Haha, how many times did four or five people look at that page and not realize that the year was wrong for all of those? Sorry about that, it should be fixed now.
Just call me "geck" because "zilla" is like a last name.

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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by MargaritaMc » Wed Oct 02, 2013 1:28 pm

geckzilla wrote:
Haha, how many times did four or five people look at that page and not realize that the year was wrong for all of those? Sorry about that, it should be fixed now.
When I saw the date, I just assumed that there had been some problem back in 2010! And, yes, it is now fixed.
M
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&mdash; Dr Debra M. Elmegreen, Fellow of the AAAS

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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by saturno2 » Wed Oct 02, 2013 2:07 pm

APOD of 02 Oct 2013, I have not image

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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by geckzilla » Wed Oct 02, 2013 2:19 pm

saturno2 wrote:APOD of 02 Oct 2013, I have not image
Did you click the October 2nd link on this page?
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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by Chris Peterson » Wed Oct 02, 2013 2:24 pm

Ann wrote:I'm going to offer a nitpick, however, and say that this picturre does not, in fact, show us all the colors of the Sun. The color violet is missing.
Not sure what's wrong with your monitor, but I'm seeing "colors" all the way off the violet end of the spectrum to the edge of human sensitivity.
Chris

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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by geckzilla » Wed Oct 02, 2013 2:48 pm

Chris Peterson wrote:
Ann wrote:I'm going to offer a nitpick, however, and say that this picturre does not, in fact, show us all the colors of the Sun. The color violet is missing.
Not sure what's wrong with your monitor, but I'm seeing "colors" all the way off the violet end of the spectrum to the edge of human sensitivity.
Same here. It's really dark. Her monitor probably doesn't show the darks very well. A lot of monitors don't. Also, it's right up against the edge so if you view the image against a white background, the contrast increases the difficulty in perceiving subtlety next to it. And, if my memory of viewing rainbows with my own eyes is correct, the violet in the linked photo of a rainbow is severely emphasized. Looking at the same image on my iPad (which has a nice screen but subject to whatever calibration Apple decided was best at the factory) the blue area leading into violet is also a lot less indigo in appearance. Like, it goes straight from blue to violet in the last two rows. Just goes to show you can't trust your monitor.
Just call me "geck" because "zilla" is like a last name.

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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by saturno2 » Wed Oct 02, 2013 3:12 pm

Very well
Thanks geckzilla

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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by Chris Peterson » Wed Oct 02, 2013 3:27 pm

geckzilla wrote:Just goes to show you can't trust your monitor.
I trust my monitor, because I use a hardware calibrator and understand its characteristics very well. But in general, your advice is good.
Chris

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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by geckzilla » Wed Oct 02, 2013 4:30 pm

Chris Peterson wrote:
geckzilla wrote:Just goes to show you can't trust your monitor.
I trust my monitor, because I use a hardware calibrator and understand its characteristics very well. But in general, your advice is good.
Most people probably don't have those devices. I don't. I don't fully trust my monitor even though it seems alright with the settings I've put it at. I operate on the assumption that everyone is looking at low quality, uncalibrated monitors with the sun shining behind them, which means that most people are probably seeing a crap quality picture regardless of what I do. :wink:

And Pat calls me a vampire for working in the dark...
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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by Cousin Ricky » Wed Oct 02, 2013 4:41 pm

Ann wrote:I'm going to offer a nitpick, however, and say that this picturre does not, in fact, show us all the colors of the Sun. The color violet is missing. The violet color can clearly be seen in this picture of a rainbow, so presumably violet is a real color of the Sun. Another color which is there in today's APOD, but which gets rather short shrift, is orange.
In addition to differences between monitors and monitor calibration mentioned by others, a fundamental problem is that all colors cannot be accurately represented on a color monitor. This is especially true of pure spectral colors.

Your monitor reconstructs colors using three primary colors to reproduce the effect on your retinas; however, not all colors can be reproduced exactly. The problem is well illustrated in this gamut diagram. There are various algorithms for finding the “nearest” color within a gamut, but the situation is analogous to projecting a round globe onto a flat map: something has to get distorted.

This is less of a problem with photographs (such as your rainbow) because typical scenes do not have saturated hues.

The orange on Mr. Sharp’s spectrum looks fine to me. I’d say that the cyan region looks a little too green, but I know of at least one algorithm that produces this effect. Other algorithms produce a bluer hue, but at the expense of brilliance. (You’ll notice that towards the blue end, the cyan looks rather muddy. This is unavoidable on an sRGB monitor, which yours probably is unless you know otherwise.)
Ann wrote:The colors of the Sun, judging from today's APOD, are sharply red, green and blue, with a few "intermediate colors". I would guess that the reason for this three-color aspect of the Sun is that it was photographed through red, green and blue filters.
I suspect the reason is Mr. Sharp’s gamut mapping algorithm, but one would have to ask him to be sure.

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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by geckzilla » Wed Oct 02, 2013 4:52 pm

Cousin Ricky wrote:Your monitor reconstructs colors using three primary colors to reproduce the effect on your retinas; however, not all colors can be reproduced exactly. The problem is well illustrated in this gamut diagram. There are various algorithms for finding the “nearest” color within a gamut, but the situation is analogous to projecting a round globe onto a flat map: something has to get distorted.
The gamut diagram always bothered me because it's subject to whatever gamut limitation of the medium it's presented on. I know it's representative but it still bothers me and confuses me somewhat. I'm no Munsell. Speaking of which, everyone should take this test. If you get a bad score, it could mean your monitor isn't doing color any justice or it could mean you're kinda color blind. http://www.xrite.com/online-color-test-challenge
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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by Chris Peterson » Wed Oct 02, 2013 4:58 pm

Ann wrote:The colors of the Sun, judging from today's APOD, are sharply red, green and blue, with a few "intermediate colors". I would guess that the reason for this three-color aspect of the Sun is that it was photographed through red, green and blue filters.
Nothing was photographed here. The image was synthesized from a large table of numeric data (which you can download and play with yourself, if you wish). No filters were involved at all. Creating an image like this involves converting a wavelength/intensity pair to a RGB value, a procedure that can be implemented many different ways, but always yields only an approximation of the color that pair would present to the eye directly.
Chris

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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by MargaritaMc » Wed Oct 02, 2013 5:19 pm

Image
This image shows the full visible spectrum, which goes shortward of the NOAO image (today's Apod) by about 10 nanometres/100 Ångström. And so shows more violet.

http://www.astrosurf.com/spectrohelio/s ... ire-en.php
This has a very nice, spread out and labeled, solar spectrum from 390 nanometres to 670 nm (3900 Å to 6700 Å)
"In those rare moments of total quiet with a dark sky, I again feel the awe that struck me as a child. The feeling is utterly overwhelming as my mind races out across the stars. I feel peaceful and serene."
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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by Beyond » Wed Oct 02, 2013 5:48 pm

geckzilla wrote:And Pat calls me a vampire for working in the dark...
Vampirzilla :!: 8-) :eyebrows:
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Re: APOD: All the Colors of the Sun (2013 Oct 02)

Post by Cousin Ricky » Wed Oct 02, 2013 11:20 pm

geckzilla wrote:The gamut diagram always bothered me because it's subject to whatever gamut limitation of the medium it's presented on.
Quite true.