[Aavso-photometry] Low-pressure sodium lights and photometry

Mon Feb 27 21:01:25 EST 2006

I responded to Bob Harmon's problem of low pressure sodium lights 
brightening the V band by emission in the Na-I 5780A doublet (a.k.a., the 
Fraunhofer "D" line"). I suggested he look into the Gunn-Thuan uvgriz filter 
system. Today, Wolfgang Renz sent me somethig regarding airglow brightening 
the background. So I should also add that the Gunn g band (which is like a 
blue-shifted V filter) also cuts off below the strong Nitrogen airglow line 
at 5577A. The filter set is well designed for keeping a "dark" background.

Michael Newberry

----- Original Message ----- 
From: "Wolfgang Renz" <w_renz at onlinehome.de>
To: "Robert Harmon" <roharmon at owu.edu>
Cc: "AAVSO-PHOTOMETRY" <aavso-photometry at mira.aavso.org>
Sent: Sunday, February 26, 2006 11:52 AM
Subject: Re: [Aavso-photometry] Low-pressure sodium lights and photometry

> Hello Bob
>
>> I'm an astronomer at Ohio Wesleyan University, which is about 20
>> miles north of Columbus. OWU owns and operates Perkins
>> Observatory (www.perkins-observatory.org), which houses a 32-inch
>> reflector. Because it's f/17, it's not very useful for CCD photometry as
>> the field of view is about 3x2 arcmin with our SBIG ST-8E. Thus, the
>> telescope is used mostly for visual observing by students and the
>> many visitors to our twice-weekly public programs. However, I do use
>> 8-inch and 12-inch telescope on site for BVRI photometry.
>
> The large reflector could be used for photometry too. You just would
> have to select your targets appropriatly. With such a small FOV and
> a good tracking/guiding mount you could e.g. concentrate variables
> with close companions, variables in globular or smaller open clusters
> etc.
>
>> To make a long story short, there is a strong possibility that a Wal-
>> Mart Supercenter and a Toyota dealership will be built within a mile
>> of the observatory to the south. The good news is that both would be
>> on land annexed by the city (pop. ~22,000) in which OWU is located
>> (the observatory is on the outskirts of town) and thus subject to 
>> lighting
>> code restrictions which would require them to use low-pressure sodium
>> lamps on 28-foot poles, as opposed to typical broad-spectrum parking
>> lot lights on 40-foot poles. (Wait until the Toyota dealer sees what his
>> cars look like under LPS light!) The bad news, of course, is that the
>> lovely yellow glow will still most likely annihilate the naked-eye views
>> from the observatory grounds and degrade telescopic views of objects
>> like galaxies and clusters.
>
> If the major light pollution source are the LPS lights, any broad band
> LPR filter that rejects the 588 nm Na emission line will help to supress
> their light output. Getting rid of HPS light output, that converts the 588
> nm Na emission line to a much broader emission around 588 nm
> and other wavelengths is much more difficult (even the IDAS LPR isn't
> ideal for this purpose).
>
> See:
> Micheal Koppelmann - High-Pressure Sodium Vapor Lamp Spectrum
> http://www.lolife.com/astronomy/na.jpg
> Christian Buil - Spectral calibration - Sky light pollution High Pressure
> Sodium lamp types (Castanet Tolosan - France)
> http://www.astrosurf.com/buil/us/spe2/hresol4.htm
> http://www.astrosurf.com/buil/us/spe2/calib2/suburb_1.gif
> http://www.astrosurf.com/buil/us/spe2/calib2/sky.gif
> http://www.astrosurf.org/buil/filters/sodium.png (HPS!)
> http://www.astrosurf.org/buil/filters/sodium_1.jpg (HPS!)
>
> SCHIAPARELLI OBSERVATORY - Light Pollution
> Light Pollution at Campo dei Fiori Observatory
> http://www.astrogeo.va.it/astronom/spettri/inq_lumen.htm
> http://www.astrogeo.va.it/astronom/spettri/pollution/inq_lum.jpg
> SBIG - DSS-7 Deep Space Spectrograph
> http://www.sbig.com/dss7/dss7.htm
> http://www.sbig.com/dss7/image028a.gif
> http://www.sbig.com/dss7/image030a.gif
> ...
>
> Christian Buil - Astronomical filter curves (LPR)
> http://www.astrosurf.org/buil/filters/curves.htm#LIGHT%20POLLUTION%20REJECTION%20POWER
> Don Goldman - Light Pollution Filters
> http://www.astrodon.com/oldsite/LPSFilters.html
> Hutech Astronomical Products - IDAS Light Pollution Suppression
> Filters, Limitations and Common Misconceptions
> http://www.sciencecenter.net/hutech/idas/lps2.htm
> Ron Wodaski - Evaluation of Hutech IDAS light pollution
> suppression filters
> http://www.wodaski.com/wodaski/IDAS_review.htm
>
>
>> I have two questions for the list. Any insight would be greatly
>> appreciated!
>>
>> 1. It seems to me that LPS lights should have a minimal effect on BRI
>> photometry, but that V might be a different story. Am I correct in my
>> thinking? Has anybody succeeded in doing good V-filter photometry
>> in the presence of strong LPS skyglow? Any tips?
>
> LPS lights has a single major emission line at 588 nm and therefore
> should show up in the images of the photometric V AND Rc band filters
> about equally (at ~ 50-70% of the max transmission of the filters).
>
> For photometry the usage of LPR filters is of course not allowed. As
> with any imaging under light polluted skies, you'll need to make longer
> exposures to reach the same SNR for photometry. With using the linear
> CCDs the effects of light pollution can be handeld much better (even
> without a LPR filter) than with the non-linear film or visually. See e.g.:
> Jay R. Ballauer - Does Light Pollution Affect CCDs
> http://www.allaboutastro.com/Articlepages/doesLPaffectCCDs.html
> Robert Bateman - LPR Problem, The effects of an LPR on a large scope
> http://www.robertb.darkhorizons.org/lpr.htm
> Christian Buil - Urban astronomical observations (LPR filters evaluation,
> spectroscopy, ...)
> http://www.astrosurf.org/buil/city/result.htm
> Tony Flanders - Aperture versus Light Pollution
> http://mysite.verizon.net/vze55p46/id1.html
>
>
>> 2. Does anybody know of references for estimating the level of skyglow
>> from a given number of LPS lights at given wattages from a given
>> distance? It would certainly help me make my case more effectively in
>> community meetings if I could give some quantitative estimates of how
>> bright the skyglow will be. Alternatively, does anybody know of any
>> photos showing skyglow from LPS lights at a single large parking lot
>> from a mile or a few miles away? There aren't any comparable facilities
>> in my area.
>
> I don't know references for estimates as they depend probably on too
> many factors. But there are a number of sites that have images with
> obvious light pollution.
>
> http://www.darksky.org/
> http://www.astrosurf.com/re/light.html
> http://dipastro.pd.astro.it/cinzano/en/index.html
> http://dipastro.astro.unipd.it/cinzano/en/sbeam.html
> http://dipastro.astro.unipd.it/cinzano/papers.html
> http://cfa-www.harvard.edu/cfa/ps/nelpag.html
> ...
>
> Sky and Telescope - Secrets of Deep-Sky Observing
> By Alan M. MacRobert
> http://skyandtelescope.com/howto/visualobserving/article_78_2.asp
> http://skyandtelescope.com/resources/darksky/
>
> Hutech Astronomical Products - IDAS Light Pollution Suppression Filters
> http://www.sciencecenter.net/hutech/idas/lps.htm
> http://www.sciencecenter.net/hutech/idas/lps1.htm
> http://www.sciencecenter.net/hutech/idas/lps3.htm
> http://www.sciencecenter.net/hutech/idas/tanaka.htm
>
>
> Clear skies
>  Wolfgang
>
> -- 
> Wolfgang Renz, Karlsruhe, Germany
> Rz.BAV = WRe.vsnet = RWG.AAVSO
>
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