What is the Sun made out of?

"The sun is a mass of incandescent gas
A gigantic nuclear furnace
Where hydrogen is built into helium

It's so ingrained in us that the Sun is a nuclear furnace powered by hydrogen atoms fusing into heavier elements that it's difficult to remember that, just 100 years ago, we didn't even know what the Sun was made out of!

Image credit: Landscape Photography by Barney Delaney.


Image credit: Stephen Lower.

Every element in the periodic table -- which was well-understood back then -- has a characteristic spectrum to it. When those atoms are heated up, the transitions back down to lower-energy states cause emission lines, and when a background, multi-spectral light is shone on them, they absorb energy at those very same wavelengths. So if we observed the Sun at all these individual wavelengths, we could figure out what elements were present in its outermost layers by its absorption features.

That technique is known as spectroscopy, where the light from an object is broken up into its individual wavelengths for further study. When we do this to the Sun, here's what we find.




What determines the strength of these lines, as well as the relative weakness of the lines surrounding it? It turns out that there are two factors, one of which is obvious: the more of an element you have, the stronger the absorption line is going to be. That particular wavelength -- 6563 Å -- corresponds to a well-known Hydrogen line.






So when we're looking at stars -- like the Sun -- we know that they come in a huge variety of different types, as a look through any telescope or binoculars will immediately show you, if it isn't clear to your naked eye.


These stars, very notably, come in strikingly different colors, which tells us that -- at least at their surfaces -- they exist at vastly different temperatures from one another! Because hot objects all emit the same type of (blackbody) radiation, when we see stars of different colors, we're really detecting a temperature difference between them: blue stars are hotter and red stars are cooler.

Image credit: Wikimedia commons user Sch.



But this was not how we always classified stars. There's a hint in the naming scheme, because if you had always classified stars by temperature, you might expect the order to go something like "ABCDEFG" instead of "OBAFGKM," right?


Image credit: Brooks Cole Publishing.


And if we go back to the Sun's spectrum, with the knowledge of what the different atoms are, their atomic spectra, and their ionization energies/properties, what do we learn from that?



Know who the scientist was who put this all together? I'll give you a hint: it was a 25-year-old woman who was never fully given the credit she deserved.

Image credit: The Smithsonian Institution.

Meet Cecilia Payne (later Cecilia Payne-Gaposchkin), who did this work for her Ph.D. thesis way back in 1925! (Astronomer Otto Struve called it "undoubtedly the most brilliant Ph.D. thesis ever written in astronomy.") Just the second woman to earn her Ph.D. in astronomy through Harvard College Observatory (where she had to move to earn one; her original alma mater, Cambridge, didn't award Ph.D.s to women until 1948), she wound up having a remarkable astronomy career, becoming the first female chair of a department at Harvard and an inspiration to generations of astronomers, both male and female.


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I have a slightly pedantic trivia fact check for you: "Why Does the Sun Shine" was recorded by TMBG, but it was written by Hy Zaret way back in 1959. It is not so great an achievement as Cecilia Payne's, but... credit where credit's due and all that.

Also, TMBG has since recorded an update to their song, entitled "Why Does the Sun Really Shine", where they make a correction: "The sun is miasma of incandescent plasma", and also comment that the previous "thesis has been rendered invalid". http://www.youtube.com/watch?v=sLkGSV9WDMA

One of TMBG's science songs is a *cover*?! Amazing!

Not as amazing as Cecilia Payne's discovery!

Sad how men fought so hard to prevent women from achieving in science, and when they went and did it anyway, fought to keep their names out of the history books. Very similar thing happened to Rosalind Franklin wrt the discovery of DNA's structure. She's the one who actually did the work to actually figure it out. But then some schmucks took all the credit and tried to relegate her to the historical dust bin.

So far so good on digging them out, and thanks Ethan for contributing! I only wonder at all the women -- and, possibly, the discoveries by them -- that are still unknown.

Still doesn't explain "OBAFGKM" ;)

By John Armstrong (not verified) on 24 Oct 2012 #permalink

Soylent green.

Which is made from humans.

Which are made of ex-star stuff.

It's a cycle of nature!

(and there's no explanation for why astronomers have a mnemonic "Oh Be A Fine Girl, Kiss Me, Right Now! Smack!" probably made up by an Arts Major as ironic humour...)

Fun fact: the corona has a density 12 orders of magnitude less than the earth's atmosphere.

So, if you wanted to describe what that first picture of Ethan's is made of, a reasonably accurate answer is: nothing. That big orange surface, all those beautiful filaments? Mostly empty space.


acceptance; and he recognized Payne's earlier work in his 1929 paper.



"Sad how men fought so hard to prevent women from achieving in science"


I like the assumption that this is no longer the case.

However, your statement implies there's been no noticeable improvement.

This isn't the case either.


Is the inside blue and the exterior red?

John Armstrong



I'm not a historian, so I defer to any who knows this history better. So Annie Jump Cannon was another woman astronomeer. "She is credited with the creation of the Harvard Classification Scheme (OBAFGKM), which was the first serious attempt to organize and classify stars based on their temperatures... The female astronomers doing this groundbreaking work at Harvard Observatory earned 25 cents per hour, which was less than what the secretaries at the university earned." wikipedia

Cannon's work came before Cecilia Payne's work.


What is the Sun made out of? Iron, if you're a crank, or easily persuaded by one.

By Mal Adapted (not verified) on 25 Oct 2012 #permalink

When we talk about those denied credit for their work, let's not forget Jocelyn Bell Burnell, who should have at least shared the 1974 Nobel Prize for her discovery of the first radio pulsars. She did get a belated knighthood, and inspired thousands of young women scientists.

By chuckinmontreal (not verified) on 25 Oct 2012 #permalink

this does not answer my question..... WHAT IS SUN'S ENERGY MADE UP OF ????

Because your question makes no sense, madoca.

Anyone trying to answer will have to make sense of it because as written it's nonsense. And therefore they will answer a question they have tried to work out as being the one that you'd say if you knew how to say it.

You'd be as well off demanding "WHAT IS FOOD'S ENERGY MADE UP OF????" then complaining when it said to be "chemical energy" that "this does not answer my question" because you didn't mean that.

i thought the sun was made from plasma

By john goins (not verified) on 06 Jan 2016 #permalink
