Reflection on experience of doing spectroscopy so far

I have now been the proud and excited possessor of a spectroscope for about a month. If you have been following my posts, you will see they clearly demonstrate my intense interest and excitement in this new area (for me at least).

Statting with the fortunatel purchase of a competitively priced and very well designed system thayvallowed me to generste spectrums virtually immediately, it also allowed me to obtain star slwctra quickly and so i did not become put off by a significant learning curve.

Thay learning, i have found, does exist and can be frustrating but rewarding too when i get something to work.

I have discovered:

I can get spectra of daytime objects eaaily and quickly by just pointing the instrument at the ibject in question. This is rally easy to do and will work well for outreach. Unlike other astronomy branches, this one can be done in the day!

I can obtain spectra of bright stars with my 80mm Equinox Pro on alt-az mount also easily and it is not too much if an issue tk hand guide the telelscope to obtain these spectra. This is not mentioned in the manual and very little about it on the internet where guided exposures are the thing but my experience shows it is effective for bright objects which can easily be seen in the 10mm eyepiece in the guiding port.

The eyepiece in the guiding port simply needs to be focused on the slit – do this in the day. Then at night focus the star to a small round dot – as small as possible. When it is over the slit the star divides in two and spectrum evident in the guiding eyepiece. This is only when over the slit. The eyepiece in the guiding port has small field of view. It is really important to ensure the finder is aligned on the scope. I might add illuminated cross hairs to help here. Not on that yet.

The situation becomes more complocayed once i start to calibrate the spectrometer. Calibration helps as it enables accurate determination of the wavelength of peaks on the spectrum amd i can consistently obtain accuracy of calibration, it appears, within 1nm. Compact fluorescent bulbs seen to be good source of light for this exercise. They come with diffuser as part of the design (the glass cover is milky). They are small and portable. I could do with making a portable rig including such a bulb to take into the field as i have found that calonration needs to be done each time I change the telescope or even the image acquisition software! Basically I suspect it is best done every night the spectrometer is used. Comparison spectrum of fluorescent lights are available from Wikipedia together with information on the wavelengths of peaks on the spectrum. Although calibration is tine intensive, it ks rewarding and leads to exciting results when you can identify peaks correspnding to specific molecules or elements.

Although using the spectrometer hand guided with 80mm Equinox Pro was relatively easy, I have found that changing to the 120mm Equinox on EQ6 Pro mount is a lot more complex and time consuming and frustrating although potentially a lot more rewarding. Changing to this set up opens up the possibility of taking spectra of much fainter and difficult to find objects and taking much longer exposures including planetary nebulae and faint stars. I have only used this set up once to date (last night), and this experience demonstrated to me that the driven moint does allow me to take significantly longer exposures without having to keep moving the scope with fine control on handset even when mount is poorly aligned. I found that using the spectrometer eyepiece to align the mount was quite difficult as the eyepiece uses light from the reflection on the highly polished metal around the slit. This is a lot less efficient than a high quality mirror with costing ps and so the image is much fainter than I would normally see in an eyepiece in a diagonal. Two possible solutions to this problem for the future are:

1. Next time I could align the mount without the CCDSPEC in the scope and then insert the CCDSPEC. As the CCDSPEC will need to be calibrated and its weight needs to be taken into consideration when balancing the scope on the mount, in practice this will mean that I need to mount the telescope on the mount together with CCDSPEC in the focuser, calibrate the CCDSPEC/QHY6 whilst attached to the scope, take the CCDSPEC out, then align the mount without rhe CCDSPEC in situ, then reinsert the CCDSPEC and do observations. This leads to quite a lengthy and complex set up process and hence I can see the advantage of having an observatory with fixed and permanently aligned telescope for spectroscopy. In addition, I am worried that the mount will have difficulty being aligned without the weight of the CCDSPEC in the focuser due to balance having been achieved with the CCDSPEC in place.

2. A better suggestion has been made by Damian. He has suggested that rather than taking the CCDSPEC on and off to align the telescope, a preferable option would be to use the excellent new laser pointer made for us by Ed as part of the three star alignment of the mount. Great idea! In addition, changing the eyepiece on both the CCDSPEC and finder scopes to illuminated reticule versions will help.

Andy

4 Responses

  1. Completely absorbed by your findings. Would love to see some planetary nebulae spectra, such as M57, M27 and NGC 7662. Gives another window on what’s going on up there ,
    Nick.

    1. I would also like to take spectra of planetary nebulae as apparently they show limited numbers of lines, mainly OIII and hydrogen (hence the use of OIII and UHC filters in observing). I would also like to directly observe (via displacement spectral lines from one side of the object to the other) rotation in galaxies & split spectroscopic binaries.
      I am getting a bit ambitious…
      Andy

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