how do astronomers know what a star is made of?

Question

if a star is say million's of light years away, how do they know it hasnt got oxygen, water an atmosphere etc, cant see much in a telescope can they?

Answer 1

They observe the spectra of light coming from the star to see what elements are there. Different elements throw off different spectra.

http://www.learner.org/teacherslab/science/light/color/spectra/
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When astronomers pass the light of a star through a spectrograph, they get a spectrum of the star. The spectrum looks like a regular rainbow of colors—except that there are dark lines in it.
What's going on?

It turns out that each element absorbs light of a particular frequency—a particular color. If that element is in the cool atmosphere of the star, those atoms will absorb the light at that color and produce the line. Each element has a specific "signature"—a specific set of lines

Answer 2

Every atomic element has an "absorbtion spectra"...dark lines that appear within the spectrum taken from the light it gives off. By analyzing the spectrum of a star, one can match up the absorbtion lines with known elements and thus deduce what the star is made of.

Answer 3

From the spectral bands in the light. Each elements has certain frequencies of light it likes to emit, and frequencies it will not. Take for instance a neon tube: it glows red when electricity runs trhough it. Fill the same tube with argon, and it will glow purple.

Each element does have its " light fingerprint" when the light they emit from being heated is decomposed by a prism. The apparatus to identify elements from the light signature is called a spectrograph.

Answer 4

Elements give off certain spectrums of light when the material is stimulated as it would be at a star temperature. By checking the colors that are being given off they can tell what elements are on the star.

Answer 5

Exactly! They cant smell it, bottle it, can't even see it properly as you say. Perhaps they've got something other than the common telescope to find things out, like maybe a blood-sucking, finger-printing super ball that brings things back in a little ruck-sack. Is that what a Pepperami is?

Answer 6

Sun is a typical star and by studying our own sun astronomer would know what other stars in the universe made of and how they evolve.

Answer 7

they study the books about different stars

Answer 8

A vote for Ronin's explanation of spectra.

Answer 9

yeh , and they can also read your mind, thats what you should never point a huge telescope at someone.... thier dirty thoughts could blow up the space observatory, like a napalm bomb

Answer 10

Because they are clever sods, see above. Sorry no more freebies tonight.