Visual spectroscopy

[Rob_K]

Just for a change of pace! Tonight I was tinkering with my telescope to make sure it was right for a public viewing night I'm assisting with on Thursday. I thought I might screw the Star Analyser grating into an eyepiece to see what I could see (if anything) of V1369 Cen (Nova Centauri 2013).

First thing I noticed in checking some bright stars is that the telescope (& eyepiece combination) wasn't really the right tool for the job. 4.5" f8 reflector at 43x was giving just too small an image scale with the spear of the spectra only a few arcminutes in apparent length. Bigger aperture at considerably more magnification would be much better.

Still waiting for the nova to clear trees, I punted on Eta Carinae. It was bright enough to throw a reasonable spear and I was pleased to see that the H-alpha emission gave a tiny little red dot at the red end! But there wasn't much else I could discern.

I had the telescope on the nova as it finally cleared the trees and spent a bit of time looking at it. The spear of the spectrum appeared to be less 'stable' than Eta Car, don't know if it was the poor seeing or not but it seemed to shift around, one second the red end strong and next second the blue. Very hard to hold for more than a moment. Nonetheless I was able to make out the H-alpha emission as a pinprick of red on the end of the spear and in a few moments of clarity I could see the bright cyan of the H-beta emission. Pretty pleased under the circumstances but probably not something I'll do regularly in the future!

Cheers -

[Jon (Jonathan)]

Fun idea.

I sometimes wonder about taking the SA100 along to a public night and putting it on the DSLR on my guidescope. The DSLR has liveview so the punters could see a spectrum of whatever it is the scope is pointed at - say Acrux, nice double star at the eyepiece, nice bright spectrum on the camera.

You reckon they'd be interested?

[Rob_K]

I've used the SA100 before at public nights - people are usually wowed by the colours thrown by stars and if you aim the telescope at a bright, tight open star cluster it can be quite spectacular through the eyepiece. IC 2602 in Carina is good at this time of year. You can explain the valuable information that spectra show but mostly people are trippin' on the psychedelia of it all!

At tonight's event there will be a First Quarter moon in the sky so it's not ideal for deep sky and I was looking for other infotainment to supply! I have a webcam and because dark adaption won't be critical I'll do the Moon, and Jupiter if it's above the treeline at the observing site. The SA100 might be good to show the double in Alpha Centauri - unfortunately Eta Carinae and V1369 Cen are too dim for that set-up (checked the other night) which is a pity because they throw such interesting spectra. Need some mag 0 to 3 stars with some big emissions!

Cheers -

[skysurfer]

Nice try. I did once Betelgeuse with my (former) 25cm Dobson and the Canon behind it and eyepiece projection with a Baader grating filter in it. I put the grating lines parallel to the motion so a 30 sec. exposure would stretch spectral lines, so no tracking is required.
I think a 4th mag star like eta Carinae is too faint and that star is so hot (class B or O ?) it does not produce easily visible spectral lines, just a continuous spectrum with faint lines. Alpha Centauri might be a better sample: same spectrum as the Sun and bright.