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I created this forum about a year ago as a place to collect spectroscopic images. I thought maybe a very brief and amateurish introduction to spectroscopy might help set some context. Caveat: I am a raw amateur with regards to spectroscopy. There are many others who are more experienced and/or who have produced better and more interesting results than I have with even more basic equipment. So this is a little bit of what I know, but if you want to learn more there are many better sources. Spectroscopy is the analysis of stars and other bodies by examining the wavelengths of light they emit or absorb. If you've performed any sort of narrowband imagining, you're familiar with emission nebula that emit Hydrogen Alpha, Oxygen-iii or Sulfur-ii emissions: very specific wavelengths of light created by very specific energy transitions within the elements' atoms. Those transitions are the basis of spectroscopy, and account for the lion's share of astronomical discoveries. The composition of stars and nebula, red shift and blue shift, star temperatures and luminosity, galaxy and star rotational speeds, etc., are all related to the spectra of light emitted by those bodies. Getting started is easy. You need some way to create a spectral image. A diffraction grating which fits your filter wheel or camera nose will do the job. Many folks start with a Paton Hawksley Star Analyser (e.g. https://www.rspec-astro.com/star-analyser/ ) . Put it in your filter wheel or in your camera nose, align it with the long edge of your sensor, and off you go. You can certainly obtain more refined and advanced equipment, but basic diffraction grating will get you started. I start by focusing with a luminance filter, and then refocusing inward a fixed amount that I've determined by trial and error. You want the lines in the spectrum to be sharp: it's okay and and even expected that the star is a little out of focus. Once you've captured a reasonable spectrum -- sharp lines, no clipping on the high (white) end of the signal -- you use specialized software to calibrate and analyze it, such as RSpec ( https://realtime-spectra.com/collections/astronomical-spectroscopy/products/copy-of-rspec-astronomical-spectroscopy-software ). There are others: I've used RSpec but you might prefer something else. Whichever way, with software assistance you can calibrate your spectrum, adjust it for your camera response, and begin the analysis. Like I said, I'm a raw amateur, so I've been satisfied with getting calibrated curves that somewhat resemble professionally developed curves for the same classes of stars. I've also played around with trying to predict star surface temperatures based on my spectra, and that's a whole area of learning in itself. But mostly, I've found it very satisfying to take a spectrum and see with my own eyes, with data coming from my own equipment, that yes: some stars have strong Balmer (hydrogen lines), some stars absorb strongly on titanium and other less common elements, Wolf-Rayet stars are wildly different, and there really is a change in spectrum as you move from hot O-class stars to the cool M-class. Maybe I'm not discovering anything new, but I'm seeing the basics of the science for myself, and it is real. That is exciting. So that's the story. I'm hoping that if there are other spectrographers lurking out there, they might add their images here, and if you decide to give it a go, I hope you'll share your results. I still like to take pretty pictures, but there is still a lot of reward in the more basic practice of collecting spectrums: your rig starts to become an instrument for collecting quantitative data, not just qualitative, and to me that's pretty cool. |
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Hi Joel. Thanks for setting up the Spectroscopy group. I very much share your enthusiasm for spectroscopy. I first got introduced to the Star Analyser about two years ago and was surprised to discover how accessible spectroscopy is to the amateur astronomer. In fact, most users here on Astrobin will find that all they really need to get started in this hobby is the diffraction grating, which compared to the price of astronomy equipment in general is a fairly small investment. I hope your group will open the eyes of other Astrobin users for this exciting niche of astrophotography. Cheers, Johannes |
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I also try to follow the spectroscopy posts to Astrobin. I find it scientifically interesting and hope to try it for myself sometime soon. Keep posting on the topic. @Joel Shepherd, I see you are using a fairly large telescope for your spectroscopy images - is there any realized benefit of the focal length for this purpose? I was thinking maybe to just try it with my Redcat since it seems like the telescope size shouldn't matter too much? |
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Thanks Johannes and Matthew - Nice to "meet" a couple other folks with interest! @matthew.maclean I'm just using the scope I have: there's really no particular need for that long a focal length (882mm with the flattener/reducer). This page has some resources on how best to position a grating and also a calculator for determining the grating will work best for your optical train: https://www.rspec-astro.com/calculator/ . Also, I should mention this mailing list/group, which is pretty active and offers a lot to learn just through osmosis: https://groups.io/g/RSpec-Astronomy . (Not trying to shill for RSpec, but they have created a ton of resources to help people get started.) @Johannes D. Clausen : I thought your name was familiar: you're an active contributor to that group. |
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Hello all, I am just getting started in Astrophotography with my Redcat51 and EQ6R-Pro mount. Back maybe 15 or so years ago I took an Astronomy class at our local community college for fun to learn a little more about astronomy. One of the things we reviewed was on the subject of spectroscopy. I found this to be one of the most interesting things we learned about in the class. When I came upon this form and then saw the link to the rspec-asto.com site, I could not believe it. That excitement started to return that I felt 15 years ago. And now seeing that I can actually record this type of data and analyze it with my own equipment is super exciting. In will definitely be following this forum and digging deeper into this subject. -Tom |
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| Hey @Tom Mihelich - Welcome to the sport and glad you tripped over this. One of the quirkier things about Astrobin is that there are forums and groups; seems like posts like this got to forums and images go to groups, or something. Anyway, if you haven't already tripped across it, here are images from the spectroscopy group: https://www.astrobin.com/groups/214/spectroscopy/ . Have fun! |
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Hi Joel, Thanks for starting this forum and pointing out some resources to get started. I am interested in doing some other activities with my equipment other than straight imaging. Including photometry. But spectrometry could be rewarding. As a biochemist, I have used spectroscopy for rather simple real world applications. But this would be much more thrilling! Alan |
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Very good initiative Joel! Hopefully I'll be able to do more spectroscopy this year, I am planning to use the old ASI1600mm for spectroscopy projects, it's going to be easier with the larger chip compared to the planetary cameras. Clear skies! Bogdan |
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Hi Joel, just found this group. Glad to know I'm not the only one doing spectroscopy, I just started with it.😀 My next projects will be, trying to see the red shift of a quasar and a galaxy. CS, Robert |
