by Marek Cichanski
I was looking at my favorite weather product - the 4km IR satellite loop - and I saw that a clear spot was coming overhead. So, I headed out to the garage and set up my ED80 - along with a new gizmo that I just bought off of Astromart.
I now have a Rainbow Optics spectroscope, and whaddya know, it works! This is a pretty slick little device. Basically, it's just a high-quality (I guess) diffraction grating mounted in a 1.25" filter cell, along with a lens that fits over the top of the eyepiece. You just screw the grating cell on to the bottom of the eyepiece, and mount the 'lens cell' over the top of the eyepiece. Voila, you've got a spectroscope. A little turn of the lens cell serves to maximize the width of the spectrum, and a little extra in-focus brings the spectral lines into focus.
Like all observing, this seemed to have a bit of a learning curve. At first I couldn't seem to see any spectral lines, but eventually I tried it on a bright enough star - Altair, I think - and it worked. I clearly saw two lines, which I think were the H-beta and H-gamma lines. I tried some other bright stars, Vega and Deneb, and saw lines in the spectra of those stars, too. Aldebaran had the most complex spectrum of all the stars I looked at. Many of the spectra showed a few distinct lines, with hints that there might be more detail. It was kind of like the way the core of a globular cluster may not be resolved (depending on the instrument), but it gives hints that it could be resolved if the seeing were better or the aperture were bigger. For an initial test on a 3" scope, it seemed to work pretty well.
I'm looking forward to trying this with bigger-aperture telescopes. I'll bet it will be great on the 18". Maybe with the 18" (or possibly the 30" at FP), it might be possible to look at the molecular absorption bands in the atmosphere of a carbon star like T Lyrae. It would be neat to look at a galaxy and try to see the continuous, star-like spectrum. And I really want to look at a planetary nebula with the grating in place. According to the Hartung book that was our bible down in Australia, you can pick out a stellar-like PN by using a prism or grating. The stars all yield spectra, but the PN stays a single image (or small number of discrete images) because it only has an emission-line spectrum. That sounds really cool. I wonder if a big emission nebula like Orion would show anything?
I even looked at the spectrum of the Sun - at night!
You can probably guess how I did it - I used sunlight that had bounced off of Mars. I put Mars in the field of view, focused the spectrum, and with a little scope jiggling (parallel to the orientation of the spectral lines) I convinced myself that I was seeing some lines.
I think this will prove to be a fun gizmo. It will be really nice to be able to use this at star parties, to show people how astronomers analyze the compositions of the stars. It will be nice to be able to show that instead of just talking about it.
Posted on sf-bay-tac Nov 05, 2005 22:15:17 PT
Converted by report.pm 1.2 Mar 16, 2006 19:22:29 PT