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How do we identify chemicals in space? For example, how did we find the cloud of methyl alcohol (aka methanol) in W3 (OH) which is 6500 light years away. I can understand a scope being able to tell something is there, but I don't see how they determine that it is not only alcohol but the type of alcohol.

Here is a link to the W3(OH): https://phys.org/news/2014-09-alcohol-clouds-space.html

But I am looking for a general answer - as to how we identify chemicals, any chemicals, in space.

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    $\begingroup$ What do you mean by W3? Could you please edit your post so that it doesn't confuse users who are unfamiliar to this term? $\endgroup$ – fasterthanlight Jan 15 at 2:05
  • $\begingroup$ The article you link to contains the answer. "astrophysical masers produce bright light at a narrow range of wavelengths." the wavelengths depend on the specific chemicals that make up the maser. $\endgroup$ – Steve Linton Jan 15 at 8:33
  • $\begingroup$ Spectroscopy $\endgroup$ – Jonas Jan 15 at 9:37
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The science that studies the problem you described, is called "spectroscopy". Every element absorbs some of the wavelengths. Same is with molecules. The spectrum is like the footprint of the molecule.

When you observe the light from emitted from some object, you see the continuous spectrum, emited from the light sources (stars, etc.). But it has some black lines present. These are the wavelengths that are absorbed by the molecules and elements. Then you compare it with different spectrums on the Earth (where we can identify the substance) and when you find the same spectrum, you know with a extremely high probability that this is the substance you are searching for.

Example for methanol: Astronomers observed the object with spectroscopy and found the spectrum with some black lines present. They compared it with various other spectra on the Earth and found out, that methanol has same spectral lines. Both measurments can be showed with a graph: https://webbook.nist.gov/cgi/cbook.cgi?Spec=C67561&Index=1&Type=IR

Spectral lines are normally showed with a spectrum (with colors) and some black lines, but this graph shows the dark lines more physically (not all is absorbed) on a graph as deep valleys.

Be aware! There may be redshift present in distant objects. That means, that the lines would shift to the red part of the spectrum. (Similar to Doppler effect.)

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    $\begingroup$ Nebula are an extremely bad example. Many actually are an example of emission-line objects which do not feature a blackbody spectrum of radiation - unlike stars. $\endgroup$ – planetmaker Jan 15 at 23:21
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    $\begingroup$ It would be good if you could specifically say how methanol was detected in this case. $\endgroup$ – ProfRob Jan 16 at 10:50
  • $\begingroup$ Correct answer that gives a general frame. Emission and different spectroscopies could have been mentioned as already commented, Plus 1 $\endgroup$ – Alchimista Jan 16 at 12:37

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