Stellar/Solar spectroscope

[dark star]

Hi, apart from making a finder scope out of an eyepiece and a binocular objective, which worked quite well, I have never made or modified any astronomical equipment, and I am not very practical or good with my hands.

However, I have become fascinated with the idea of trying star spectrography, where the light from a star is split by going through a prism or grating to show lines from which can be worked out the stars chemical composition, if I have understand it correctly.

As I do not want to immediately get into complicated CCD cameras etc. which I have almost no understanding of and as I enjoy visual observing, I am interested in trying to construct a star spectroscope using a glass prism, in order to see the emmission lines (I think this is what they are called.)

I have tried reading various web sites about star spectropscopy, but these tend to be rather technical and concentrate on the use of cameras.

On one site, I think it was Maurice Gavin's spectrometry site, there is a description of the use of a right angle glass prism from some binoculars being used with a camera, attached to the front of the lens. This is called an objective prism spectroscope. I have also read various descriptions of the use of slits to concentrate the spectra.

Does anyone have any idea how to construct a spectroscope using a glass prism and for example a finder scope and possibly a slit constructed from razor blades? I do not need palns etc. just a rough idea where everything should go and what equipment I need, so I can experiment.

I am also interested in constructing a solar spectrograph. Also on Maurice Gavin's website there is a description of a solar spectrograph constructed using a mirror to reflect the sunlight into some kind of cylinder/eyepiece and then in to a grating. i have read about gratings and am thinking about buying one, but I am curious if it is possible to use a prism from a binocular instead. On the website the light is then directed in to a camera, but it is stated that a small finder scope can be substitted for visual observations.

Obviously I need to be sure if I use a prism this is not dangerous due to the power of the sun! Presumably using a grating splits up the suns rays so they do not present a danger, would a prism have the same effect? Has anyone done anything like this to study the sun or know anything about ?

I realise that this is a minority interest, but if anyone has any ideas or knowledge about any of this I would be grateful for advice.

I also realise that gratings are probably more useful for more serious spectrography and that it is possible to buy the Star Analyser, which uses a grating. But I would like to experiment with prisms first!

Also, I understand that scientists first used prisms to analyse stars, and I would find it interesting to repeat this if only to a limited extent.

Sorry if I have gone on a bit, but it is quite complicated to explain!

I will try contacting the specialised sites dealing with spectrometry if necessary, but I wanted to check if there is anyone on Stargazers Lounge who knows a lot about this subject first. (Or at least more than me!).

Thanks in advance for any help or advice.

[Psychobilly]

Merlin66 (Ken) is your man... I am sure he will pop into this thread...

Peter..

[Merlin66]

You can use a prism ( a 60 degree is best) or a grating (transmission or reflection) to diffract white light into a spectrum.

For solar work you need a slit ( this forms the "lines" in the spectrum) a couple of pencil sharpner blades work as does the reflection from a needle.

There's a couple of good general websites; you've already found Maurice Gavin.....

WPO main spectrum page

Fulvio Mete

Home Page

Samir Kharusi

Spectrograph

John Blackwell

Regulus! Astronomy Education: Spectroscopy

Christian Buil

Spectroscopy, CCD and Astronomy

and Y! groups

astronomical_spectroscopy : Astronomical Spectroscopy for Amateurs

staranalyser : staranalyser

Hope this helps.

Ken

[FraserClarke]

Obviously I need to be sure if I use a prism this is not dangerous due to the power of the sun! Presumably using a grating splits up the suns rays so they do not present a danger, would a prism have the same effect? Has anyone done anything like this to study the sun or know anything about ?

In this sense, prisms and gratings do the same thing; they both disperse the light into separate wavelengths. Whether the resulting spectrum is dangerous or not depends on how much dispersion there is (more dispersion == lower light intensity per unit area == safer). I have no idea off the top of my head how much one would need to disperse sun light to make it safe.

With a grating, you'd also need to be careful to block the 'zero order' -- a fraction of the light goes straight through without any dispersion.

Prisms tend to be lower dispersion than gratings (but not always), so which technology you use depends on the spectral resolution you're trying to achieve.

[Merlin66]

The normal slit width used to form a spectrum of the Sun is about 20 to 30 micron wide; this in itself significantly reduces the amount of heat/ light energy getting through to the prism/ grating. When this light in turn is dispersed across the whole width of the spectrum the intensity is further reduced.

With a 300 or 600 l/mm grating on a 135mm lens, using a 20 micron slit, there's no problems visually observing the spectrum with a 12mm eyepiece.

[dark star]

Thanks a lot for all the information. I will spend some time looking at the spectropscopy websites and absorbing what you have told me.

I have found some educational websites where it is possible to buy glass prisms.

I will post again once/ if I manage to construct something and if I get stuck!