wpo - lo-res lunar spectrograph
astro-optics page
The
schematic and photos show the principle of a simple low resolution spectrograph
[dispersion 16A/pixel] with some test spectra of Mercury [Hg] and
Neon [Ne] emission sources recorded onto the Starlight Xpress MX5c one-shot
colour camera.
It uses a sewing needle [currently held in place with Blutac] as a reflective slit diverting a 20 micron wide sample of light through 90 degrees onto the transmission grating for dispersion and then through a lens to focus the slit [and spectrum] onto the CCD. An old 32mm fl f1.7 half-frame camera lens used here but any single achromat ~30 - 50mm fl [or better two lens of ~60 - 100mm fl - one placed either side of the grating] will serve to image the slit onto the CCD. A True Technology flip mirror box supports the components but an old star-diagonal [less prism/mirror] could serve equally well.
Regular photo-extension tubes [10mm, 20mm, 30mm] provide in combination the precise separation of the optics. The position of lines in the spectrum can be measured from either the zero order image [here to right] or a Hg lamp on the telescope side of the reflective slit. An eyepiece behind the needle is used to view the scene - the needle itself is silhouetted against the moon/sky and occults the target area recorded in the spectrogram.
The devise was requested by Dr Tony Cook of the BAA Lunar Section for possible TLP surveys but may have other applications for extended or point [stellar] sources.
2001
Sept 4: More spectra obtained today
including the full moon rising in east - showing additional Telluric absorption
lines from the long light path through the earth's atmosphere. Whilst
the moon was hidden in cloud emission lines [intially though to be the
PC monitor 15 ft away] proved in longish exposures to be sodium D1/D2 skyglow
on the cloudbase - I think Mt Wilson Observatory once used skyglow pollution
for calibrating stellar spectra!
More results to be posted soon.
