View Single Post
  #3  
Old 25-11-2019, 06:13 PM
JimIrish (Jim)
Registered User

JimIrish is offline
 
Join Date: Oct 2016
Location: Junabee, Q., 4370
Posts: 8
Quote:
Originally Posted by Merlin66 View Post
Jim,
I record airglow and background street lights etc. every time I collect data!!!!

Not sure how successful you would be with just a grating in the telescope.
You'd certainly pick up a background, but at a very low resolution.

I use a slit spectroscope on a C11 @f10 and usually 10 min exposure subs with an ATiK 314L camera. Due to the slit the emission for lamps etc appear as definite emission lines. For my work I just remove them using the background removal tool in BASS project.
Walker in his "Spectral Atlas", Section 31 shows a typical "night sky" spectrum.
His example is dominated by Hg, Na and [O I] at 5577A. The airglow at 6300A is missing...
I would think light pollution may be a worse factor than airglow, but I'm no photometric expert.
https://en.wikipedia.org/wiki/Airglow

In Henden & Kaitchuck "Astronomical Photometry, Chapter 9.6, p 229 they discuss airglow and light pollution.
Their conclusions (p231) ""...the light of the night sky is not constant...and therefore will always limit the accuracy of your measurements....
...measurements redward of the V filter are strongly affected by the varying night sky and should be avoided until experience is gained with the UBV system.
...The night sky variations will probably never be noticeable in your photometry, but knowledge of the possibility of these errors should be filed in your mind for later reference.""
Budding & Demican "Introduction to Astronomical Photometry" don't seem to even mention airglow......

Not sure if this helps but if you do need spectra let me know.
Thanks, Ken. I may use narrower band filters than G, B and R, with flatter spectral response. And point at the South Celestial Pole, so there's little "contamination" by starlight, though there'll be a calibration issue. I'm 12 km from the nearest town (popln. 12,000) and Brisbane is in the opposite direction so hardly affects the SCP. Nearest neighbours are well-behaved and more than 500 metres away. Surprised you only get low intensities for airglow lines with a C11. If not a grating, what might improve my resolution, ie, S/N?

I was aware that Budding and Demican didn't mention airglow, but will consult the other text you quoted.

My copy of Walker has wandered. I may have to buy another.

Will you be attending NAACA at Easter?

Jim Irish
Reply With Quote