Couple of questions for clever people about the sun (in Off-topic)


Mythology March 27 2010 3:39 PM EDT

Okay, the sun,

1) Why is it yellow?

2) Does it appear yellow yet give off pure white light?

3) Does this mean everything we look at in daylight is "a bit yellower" than it would be in pure white?

4) Are there stars out there that appear like at close distance (like we are to our sun) white?

5) Would things look different on a planet with a white star (if there are such things) than to here?

Thank you!

Gandalf March 27 2010 3:41 PM EDT

Interesting q's Myth, I'll be learning all about that stuff next year :)

Will be nice to see the answers.

AdminNemesia [Demonic Serenity] March 27 2010 3:47 PM EDT

If I remember this correctly the sun appears yellow because even though it releases light from the full visible spectrum and beyond it releases the most energy in the yellow spectrum.

I do not think there are any pure white light stars, this is because stars release energy on a spectrum and they release different amounts at different spectrums. So one releasing more energy would shift more towards purple and ultraviolet while one releasing less energy would look more red.

Admin{CB1}Slayer333 March 27 2010 3:58 PM EDT

The photosphere of the sun and the atmosphere of earth both absorb small amounts of the light spectrum which creates a small imbalance in the spectrum that we actually see; thus, yellow.

The core of the sun emits a full spectrum of light, however a lot of that spectrum is absorbed by the inner layers of the sun.

I do not believe there are white suns, because they all seem to follow the same structural patterns, and thus all suns are subject to the full spectrum they produce being absorbed by other layers of the sun.

Mythology March 27 2010 4:00 PM EDT

are you saying the sun isnt yellow if viewed from space?

Admin{CB1}Slayer333 March 27 2010 4:01 PM EDT

It is yellow, just less yellow. (A tiny bit less)

QBRanger March 27 2010 4:04 PM EDT

Actually, the Sun isn't yellow. Seen from space, the Sun looks almost pure white. The Earth's atmosphere blocks some of the spectrum of light coming from the Sun so that it appears yellow from here on the surface of the Earth.

As you might know, the light from the Sun isn't any one color. It's actually a collection of light from almost the entire electromagnetic spectrum. The gives off light in the radio spectrum, infrared, through the visible spectrum and even into ultraviolet and X-rays.

When we see the Sun, we're seeing an average color of all the photons hitting our eyes. Some of those photons are red, others are yellow, some are green and others are blue. But when you average the color of them all, that's when we get the white color of sunlight (seen from space). Now, when those photons pass through the atmosphere, some of them are absorbed or scattered away, so we see the more yellow color.

The Sun's surface is 5,800 Kelvin. It's this temperature that defines what color of light is being emitted by the Sun. If the Sun was cooler, like a red dwarf, then it would appear more red. And if the Sun was hotter, then it would look bluer.

Mythology March 27 2010 4:08 PM EDT

When you say almost white, you mean like 99% white or?

Demigod March 27 2010 4:08 PM EDT

I was about to post that the sun is a quarter helium, which burns orange (and most of the rest is clear burning hydrogen), but I like Ranger's answer better.

Demigod March 27 2010 4:09 PM EDT

http://cs.astronomy.com/asycs/forums/t/31281.aspx

ScY March 27 2010 4:12 PM EDT

1) Why is it yellow?


The color of a star basically depends on the temperature of its outer layers.
Typically stars which have an outer temperature between 5,200 Kelvin οΎ–6,000 Kelvin are 'yellow'
2) Does it appear yellow yet give off pure white light?


Every star emits electromagnetic radiation. This radiation ranges from every frequency in the electromagnetic spectrum.

3) Does this mean everything we look at in daylight is "a bit yellower" than it would be in pure white?


Nope. The color of an object is a characteristic of what ranges of visible light that the object absorbs or reflects.
4) Are there stars out there that appear like at close distance (like we are to our sun) white?


White stars generally have outer surface temperatures between 6000K -10000K. The distance the observer is from a star is mostly irrelevant as long as you are in visible range of the star (able to see it). A black ball is black if you are 10 meters from it or 100 meters.
5) Would things look different on a planet with a white star (if there are such things) than to here?


If by 'Look' you mean would objects be whiter or some different color than they are here->nope. But a planet orbiting a white star would most likely have drastic differences from earth-- the earth is a very special planet which are perhaps not common to the universe. Changing the sun type would most likely cause earth-like characteristics to cease to exist in the planets orbiting it. But there are many variables to this problem, and if you really are interested you could take a bunch of basic physics courses.

AdminShade March 27 2010 4:13 PM EDT

The colour comes from the radiation emitted by the elements present in the sun itself.

for example (not sun related), sodium emits at 285 nm which we see aa a colour of yellow

AdminShade March 27 2010 4:15 PM EDT

Perhaps a counter question to you Myth:

why is the sky blue and when you look into the distance, that is blue as well? ;)

Lochnivar March 27 2010 4:17 PM EDT

Of course our brain auto-white balances things too... so what we 'see' isn't necessarily what we 'see'... playing around with a temperature white balance on a digital camera illustrates the brain compensation nicely.

Cube March 27 2010 4:33 PM EDT

http://astronomy.fm/skylogs/spaw2/uploads/images/sky-safari/HR%20diagram%20NAU%20bt2lf1509_a.jpg

This is a diagram that relates the size of a star with the dominant spectrum. The sun's dominant color happens to be yellow due to it's size/temperature.

However, all stars emit all kinds of radiation, in other words a full spectrum and more, so it would look white.

Cube March 27 2010 4:38 PM EDT

A few clarifications

The luminosity, temperature, and size are all related on the diagram. The spectrum is related to the temperature, so there's a lot of factors contained on the diagram. This has to do with the fact that all stars are essentially made out of the same building blocks, so you can encapsulate all these variables on one diagram.

Mythology March 27 2010 5:45 PM EDT

Thank you all very very much for the information, very much appreciated :)

And whichever admin somehow managed to squeeze an "n" onto the topic title :)

Sickone March 28 2010 8:18 AM EDT

Sickone March 28 2010 8:26 AM EDT

P.S.

There is no such true color as "white".
Things APPEAR to be "white" if there is enough of every component of light that the three types of human cone cells react best to (blues, greens and reds), and if it's noticeably brighter than anything else around.
That's why most photo devices put so much emphasis on "white balance", because "white" is a SUBJECTIVE color, not an objective one.
We perceive something to be "white" one moment (the "brightest" thing around with enough of all blue/green/red in its color spectrum), and in different lighting conditions, even if the spectrum of illumination could have radically changed meanwhile, we still perceive the same thing as "white".
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