Spectroscopy for Amateur Astronomers and Educators: Reviewing Rspec

Arcturus spectrum from RSpec. Credit: RSpec

The spectra of stars have fascinated me since I started in astronomy in the 1960s. Those dark lines tell you what stars are made of. But the gadgets to do spectroscopy back then were out of my reach.

Enter Rspec, “real-time-spectroscopy,” which promises to make spectroscopy not just workable with an amateur-class telescope but easy. The software, along with a small diffraction grating, the StarAnalyser, allows you to produce stellar spectra with your telescope (or even a standalone camera) and analyze them.

Rigel and its spectrum in real-time with RSpec. Credit: RSpec

After sitting through the excellent instructional videos created by RSpec’s creator, Tom Field, I could hardly wait to get Rspec going with my telescope and camera. Almost any camera will do; I chose a ZWO ASI-120MC video camera.

When I plugged the ZWO into the PC and started Rspec, the program immediately recognized the camera and indicated it was ready to record video. I could have used any program for recording, saved the video to disk, and opened those files with Rspec, but being able to do everything with one program seemed simpler and easier. Since I was embarking on an exploration of the unknown—spectroscopy—I definitely wanted “simple” and “easy.” 

Edmund Scientific Star Spectroscope. Credit: Rod Mollise

I chose to use my Celestron Edge 800 Schmidt Cassegrain, Mrs. Emma Peel, on a Celestron Advanced VX German equatorial mount. The Rspec website indicated more focal length was better than less for spectroscopy, and the telescope’s 2000mm of focal length fit the bill. I screwed the StarAnalyser grating onto the camera’s 1.25-inch nosepiece and thought I might be ready to go.

OK, rubber meets road time. Another tip from the website suggested starting with a bright A (spectral type) star. The calibration process that comes later uses one of the Balmer series of spectral lines of hydrogen, the h-beta line, and that is strong in A-type stars.  Alas, there weren’t any A stars immediately available on that early winter evening. Rigel, however, was well placed in the east. Rigel is a B star, not an A, and the Balmer series is a little weaker in B stars, but I thought it would do.

The author’s ZWO ASI-120MC camera mounted on the Celestron Edge C8. Credit: Rod Mollise

After traveling to my observing site, setting everything up, and getting Rspec running and talking to the camera, actually taking the spectra and recording the colors of the stars was anticlimactic. When the AVX finished its slew to Rigel and I clicked on Rspec’s Live Video tab, there was Rigel and the little rainbow of its spectrum. What was really cool? In the main display area of the program, I was seeing the graph of the star’s spectrum—live. So that’s what Mr. Field meant by “real-time spectroscopy” (in modern, computerized spectroscopy, a dip in an X-Y graph indicates a spectral line).

By the time Rigel was in the can—several 15-second sequences of video saved to my hard drive—the night was getting older and colder. The graph looked pretty detailed, but I’d wait till the next day to find out if it was good or bad. I shot a few more bright stars including Capella and Sirius, an A-type star, which was finally up, packed everything in the truck, and made tracks for the warm confines of home.

The next morning, I began what I was pretty sure would be the hard work:  processing and analyzing my video sequences. I’d learned how to do that by watching Tom’s above-mentioned instructional videos, and I followed the steps outlined in Rspec’s PDF instruction manual.

With Rspec running, the first step is to open one of the saved videos. When it is onscreen, rotate the image with a slider control until the star is on the left and the spectrum on the right, as seen in the Rigel image here. With that done, pause the video, scroll through the frames with a second slider, and pick what appears to be a good, well exposed one.  Finally, the big job, calibration

Sirius calibrated on RSpec. Credit: Rod Mollise

I had a spectrogram – an image of a star’s spectrum – and I had a graph of that spectrum showing the dips that represent absorption lines. However, the X axis was in pixels, not angstroms (an older measure of the wavelength of light that has been mostly replaced by nanometers), and was utterly useless for determining the wavelengths of those lines. Wavelength is what determines the elements they represent. Calibration converts those pixels into angstroms.

I opened the program’s calibration tool and clicked on the big spike on the far left of the graph, which represents the star itself rather than a feature of its spectrum. Next was the tough part. You must click on the dip that represents the hydrogen beta line on the graph. Referencing the videos and images on the Rspec website, find the first big valley to the left of the spectrum’s peak (the actual spectrum part of the graph, not the peak of the star). Despite Rigel being a B rather than an A star, the H-beta line was easy to see. Done, I clicked “apply” and hoped for the best. 

Sirius’ absorption lines labeled with RSpec. Credit: Rod Mollise

Finally, the big payoff, what all this has been for. Select “elements” on the program’s top toolbar, which produces a window with various selections. Choose “hydrogen Balmer series,” which causes vertical lines representing the hydrogen lines to be overlaid on the graph. Does the line for H-beta run through the dip in the graph you chose as the H-beta line? Do the other Balmer lines also coincide with dips on the graph? If so, you have been successful. 

In my case, I thought I did pretty well. Some of the dips didn’t line up perfectly with the Balmer line overlay, but I was pretty sure that was a result of me not clicking precisely on the H-beta line. I also think the poor wintertime seeing hadn’t helped. But bottom line? It worked. Rspec actually worked. I could now bring up other element identifiers and explore the stellar atmosphere of Rigel. Me. With my garden variety SCT and 100-dollar camera. 

The Star Analyser. Credit: RSpec

The next session started, once again, with Rigel. I shot a couple of short sequences, moved on to Sirius, and then Capella. Seeing was pretty good, and even “live” the H-beta dip in Sirius’ spectrum was unmistakable. It almost seemed too easy. I double-checked that Rspec had saved my video sequences successfully—it had—and called it a night. 

Analyzing the spectra the next day, I took some care to click on the peak of the star’s spike and the bottom of the H-beta valley, but I wasn’t obsessive about it. When I applied the Balmer lines overlay, I was pleased to see they lined up nicely. Finally, I saved my spectrum (which the program calls a “profile”) so I could come back to it later to further explore Sirius’ makeup. I was amazed it was so easy to operate Rspec. That says one thing about the user interface: “Intuitive.” The program works well and has a professional feel. With the recently added presentation manager you can now even have two profiles onscreen at once.

Should you buy it? If you’re curious about spectroscopy, yes. Also, yes if you’re just ready for an astronomy change-of-pace. Rspec is something different.  If exploring the colors of the stars sounds interesting, get Rspec. You’ll thank me.


MSRP: Software: $109, Star Analyzer: $195



About Rod Mollise

“Uncle” Rod Mollise, a Contributing Editor at Sky & Telescope magazine, is familiar to amateur astronomers as the author of numerous books and magazine articles on every aspect of astronomy, amateur and professional. He is most well known, however, for his books on Schmidt Cassegrain Telescopes, SCTs, and especially Choosing and Using a New CAT (Springer), now in its second edition, which has become the standard reference for these instruments. In addition to Sky & Telescope and his books, Rod’s writing can be found in his popular online blog, Uncle Rod’s Astro Blog. Somehow, he also finds time to teach astronomy to undergraduates at the University of South Alabama in Mobile, and to voyage the night sky with his beloved telescopes.

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