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Is it practical to build a DIY spectroscope that can clearly show absorption lines from the Sun? "Practical" means that the kit can be made at home or relatively cheaply bought (less than £200) and attached to a small home telescope. "Clearly show" means you can actually see dark lines.

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Yes, you can make a spectrograph using little more than an unwanted DVD disc and a cereal box. If you are careful enough and look at the second order diffracted spectrum then the Fraunhofer lines can be imaged. An example is here, but there are many resources describing various ways to set this up.

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    $\begingroup$ Thanks - I presume that a prism could also be used instead of a diffraction grating? $\endgroup$
    – Slarty
    Commented Jan 15 at 18:16
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    $\begingroup$ My answer suggests using a DVD. If you use a prism you are unlikely to get high dispersion and would need a long focal length camera. @Slarty $\endgroup$
    – ProfRob
    Commented Jan 16 at 6:30
  • $\begingroup$ With all these references to Fraunhofer, and the wish to see the results of his experiment, It's recommended to re-create his experiment equipment, an element of scientific history that ended the debate about the sun being a giant ball of tar. I figure he used a prism... Soon after they were developing early spectroscopes: google.com/search?q=early+spectroscope+design here is a history of early spectroscopy equipment youtube.com/watch?v=TFP55200MPY $\endgroup$ Commented Jan 22 at 2:54
  • $\begingroup$ If you use a prism you need to focus the light after it: physics.stackexchange.com/questions/168793/… $\endgroup$ Commented Jan 22 at 3:01
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Done it. Small home telescope isn't a good start though. Project an image of the Sun on a slit with a high F number objective (so the slit doesn't melt). Then collimator lens -> reflection grating -> second objective focusing on translucent viewing screen. Three inexpensive lenses and an inexpensive grating. Might have the plans in a notebook someplace, but it's been a few decades...

Edit in response to comment.

A traditional spectroscope is like a camera: it takes a picture of something. The difference is that the image is displaced depending on the wavelength of the light. Here's an example of an x-ray spectrum of a supernova remnant obtained without a slit. It's difficult to disentangle it to figure out how much emission from each element is coming from where in the nebula.

So, common practice is to focus the incoming light on a slit, and make an image of that. Then, each of the displaced images looks like a line, whose position corresponds to its wavelength. Different wavelengths are separated.

And that's why we call resonant features in spectra "spectral lines". The terminology has stuck even for other sorts of spectrograph that don't use slits.

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    $\begingroup$ Thanks, I will have to try it. Noobie question what does the slit do / prevent? $\endgroup$
    – Slarty
    Commented Jan 15 at 18:33
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You can make an extremely accurate spectroscope for the sunshine through a telescope and prism... The prism changes the beam of light at the end of the telescope into a rainbow and you should be able to see small black lines inside of the rainbow... Early apparatus would have looked a bit like this, obviously don't put your eye on it, but I can't find Fraunhofer's precise rig, these are precision DIY spectroscopes: google.com/search?q=early+spectroscope+design

For the sun you need a cardboard with a slit after the prism to focus the lines because otherwise they become burred: https://physics.stackexchange.com/questions/168793/sun-spectroscopy-home-experiment

If you want some related history, this video describes some related events: youtube.com/watch?v=TFP55200MPY

Don't explode your eyeball though learn the proper method of aligning a prism in front of a telescope and shining the rainbow onto a wall to see the black lines that are absorbed by the sun's cooler peripheries.

The small black lines correspond to non-ionized elements in the Halo of the sun which are absorbing the pure bandless white light of the sun at specific wavelengths...

The sun does not have any lines though because it's a plasma of ionized material without electron orbit distances of a regular geometry...

The method was invented by Bundsen and his colleague and they also used the system to measure the spectra of burning of elements like sodium in front of a plasma lamp spectrum to recreate what the sun spectrum looked like.

You can find info about Bundsens lab tool on the web, "cathy loves physics" episode on Bundsen is a chronology of the discovery of what the sun chemistry is.

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    $\begingroup$ en.wikipedia.org/wiki/Bundsen ? Perhaps you mean en.wikipedia.org/wiki/Robert_Bunsen ... $\endgroup$
    – PM 2Ring
    Commented Jan 16 at 6:48
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    $\begingroup$ "The sun does not have any lines though because it's a plasma of ionized material without electron orbit distances of a regular geometry..." what does this mean? Are you denying the existence of Fraunhofer lines? $\endgroup$
    – ProfRob
    Commented Jan 16 at 16:46
  • $\begingroup$ A plasma does not have lines it is a continuous spectrum. The Fraunhofer lines are not from the plasma, that's what I wrote. Besides, bunsen's equipment using the telescope and the prism answers the question. Fraunhofer did not understand what the lines corresponded to. 45 years later, Kirchhoff and Bunsen noticed that several Fraunhofer lines coincide with characteristic emission lines identified in the spectra of heated elements. It was correctly deduced that dark lines in the solar spectrum are caused by absorption by chemical elements in the solar atmosphere $\endgroup$ Commented Jan 16 at 17:55
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    $\begingroup$ Then clarify that in the body of the answer. Also the first paragraph could lead a naive reader to try something unsafe. $\endgroup$
    – Mike G
    Commented Jan 17 at 11:45
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    $\begingroup$ A plasma does not have lines? Huh? When we study plasmas, we commonly use spectral lines as diagnostics of temperature, density, velocity, excitation conditions, and composition. Plasmas have lots of lines. $\endgroup$
    – John Doty
    Commented Jan 22 at 3:06

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