This page discusses some examples of the kinds of projects that can be done with a low resolution diffraction grating like the Star Analsyer or the Rainbow Optics Star Spectroscope.
Great introductory lectures on spectroscopy: Tom, RSpec’s author, is now available as a speaker to your club. Read more about these very popular talks by clicking on this link or the image below.
Some of the projects below require telescopes. But, there are quite a few that you can do using a simple DSLR camera, like that Canon camera you have sitting upstairs! You can even use your cell phone to capture spectra!
You can post questions about these projects on the RSpec Yahoo forums (link) or email us from this contact form.
Characterizing Star Types: Using a modest telescope, capture a spectrum of one of each type OBAFGKM star. Comparing them, you will be able to discern differences in the absorption lines. You could also compare the spectra curves to those in the RSpec Reference Library to determine the approximate star types. This would make an excellent science project.
Below is a sample of some the excellent work done by Torsten Hansen, using a Star Analyser grating and an Imaging Source video camera. From top to bottom, the spectra are in OBAFGKM-0rder, starting with “B”. Notice for example, that the cooler stars near the bottom have a lot of wide absorption lines in the red end of the spectrum. That’s the absorption from the molecule Titanium Oxide.
Also notice, for example, that the Hydrogen Balmer (beta) absorption line at 4861 Angstroms gets stronger as as you move from hot B stars to A. It then weakens as you move further down to to cooler stars. This particular Hydrogen transition isn’t as predominant in the hottest or coolest of stars. See? There’s lots to learn here:
Difference in Star Types (OBAFGKM) are clearly visible in these spectra
Detect the Emission lines on an Emission Nebula: An emission nebula is surrounded by a gas shell that is excited (like a florescent light). Below is a spectrum of the Saturn Nebula clearing showing its emission lines. The Orion Nebula (M42) would have a similar appearance.
Emission lines of a Nebula!
Detect the Spectrum of a Super-giant: The super-giant P-Cyngi shows distinct emission lines in the image below. Notice how they differ from the Saturn Nebula above. (François Teyssier)
Emission lines of Super-giant!
Detect the Methane bands in Neptune or Uranus: The image below by Paul Tervit shows the absorption by Neptune’s atmosphere:
Neptune's Methane Absorption Bands
Detect the Red Shift of a Quasar that is 2 billion light years away: Robin Leadbeater, using only a modified webcam and 9” Cassegrain captured the spectrum below in an urban setting. The red shift of QSO 3C 273 due to the expansion of the universe is clearly visible! For more details and lots of other great examples of what you can do with both low and high resolution spectroscopy, see Robin’s site: link.
Red Shift of a quaser 2 billion years distant!
Wolf-Rayet Stars: The spectrum below is a fascinating view of a Wolf-Rayet star by Janet Simpson using just a Canon 350D DSLR and 85 mm lens, 30-second exposure with AstroTrac mount. She used the Star Analyser 100 for a grating. (For mounting hints, see this link.)
Wolf–Rayet stars are a normal stage in the evolution of very massive stars, which continually eject gas into space, producing an expanding envelope of nebulous gas. Notice the wide Carbon emission bands! Their width is attributed to the Doppler effect because the gas surrounding these stars is moving with velocities of 300–2400 km/s along the line of sight.
The characteristic emission lines are formed in the extended and dense high-velocity wind region enveloping the very hot stellar photosphere. This produces a flood of UV radiation that causes fluorescence in the line-forming wind region. This ejection process uncovers in succession, first the nitrogen-rich products of CNO cycle burning of hydrogen (WN stars), and later the carbon-rich layer due to He burning (WC & WO stars). Most of these stars are believed finally to progress to become supernovae of Type Ib or Type Ic. (Wikipedia link)
Yes, it doesn’t take a ton of gear, skill, and dark skies to do this kind of work! It’s images like this that we find so enormously exciting.
View the powerful glowing winds of a Wolf-Rayet star!
Solar Spectroscopy: You can have fun doing astronomical spectroscopy and still get a good night’s sleep! Use a ball bearing or a sewing needle with a dark backdrop to get an spectrum of the sun. Be careful of your eyes. Never look directly at the sun or its reflection.
David Haworth has published a creative and inexpensive apparatus that you can easily build to capture spectra of the sun. (For details, see his site: link.)
David Haworth's simple solar spectrograph uses a sewing needle
The above spectrum, when processed in RSpec, clearly shows the sun’s Fraunhofer lines:
The Sun's spectrum from a simple needle spectroscope
Comet: Rainer Ehlert captured this lovely spectrum of a comet. Notice the variety of complex molecules. These complex molecules are thought to have provided the raw material that formed the building blocks of life when they pelted the Earth during its early history.
Supernova: Below is a wonderful spectrum of a supernova imaged in early September by David Strange in the UK. The deep absorption marked as Silicon II is an indicator that this is a Type Ia supernova. At the time he took took this image and created the profile, David had been using RSpec for just over a week.
What continually amazes people is how little integration time is needed to capture spectra. This spectrum was captured on a 9″ SCT, with only 30 twenty-five second images! We’re not talking about hours of integration time here, nor large aperture. Dark sky sites aren’t required either – spectroscopy is considerably less affected by urban light pollution than visual imaging.
To download the original FITS image (courtesy of David Strange), right-click this link . Video that discusses calibrating this image: link.
Just a final comment on the above spectrum and calculation: this is jaw-droppingly exciting stuff. Imagine: a backyard telescope measuring the Doppler shift of a supernova!
It’s likely that you already have the telescope, camera and skill to do this kind of thing yourself! Sit back and really appreciate just what the examples on this page show is possible. Have you always wanted to do a bit of science? Spectroscopy is a way you can start to honor your “inner scientist.”
Gas Tube or Standard House-light spectroscopy: You don’t need to buy a telescope or expensive grating to do spectroscopy! This Google search (link) will show you how to easily build a spectroscope with a DVD and some cardboard. Then, use your cell phone camera to take some images or video. (Contact us for details on how to get IPhone .mov videos into RSpec.) You will be able to differentiate different light sources from one another. This could be a great science project! Want to see what’s possible? Click on this link.
Flame Emission Spectroscopy: No, it’s not astronomy either, but you can do it in the comfortable indoors during the winter! The light emitted from glowing gases can be used to identify the gas. Here’s a link that discusses this further. This would be a good school science project. You could do it with the DVD spectroscope described above. Be careful with open flames!
Do you have an spectrum we could post here? Low Resolution spectroscopy can also be used to identify variable stars types, novae and the occasional bright super-novae (as shown above with SN2011fe). If you have samples of this kind of work, or other low resolution spectra of any type that you’d like to see posted here, contact us.
All images used with the permission of their respective authors.
