Los Angeles and area

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In order to subtract man-made emissions from their data, professional astronomers analyze and catalogue sky-glow. And although that information can be found by anyone, the data are from darker observatories commonly removed from strong urban sky-glow that many amateurs face.

So there's a disturbing gap in the knowledge of actual or tangible urban sky-glow spectra in any astronomical literature, online or elsewhere. For the big cities, dated estimates of sky-glow are often found and the only assumed sky-glow emissions are the sodium and old mercury spectral lines. Just by glancing at the spectra above, astronomers need worry about a great deal more.

Twenty years into the millennium, it's time to update the info on the new spectra found in urban sky-glow.


Using the easier overcast method, I visited other cities to secure their "up-light" signatures. For such overcast sky-glow spectra, the scattering is always independent of any wavelength and representative of the local up-light.

Downtown Ottawa Up-light Spectrum 2017

Is LED lighting good? Is it bad? How can you tell? Downtown Toronto's OVERCAST up-light spectrum:

Downtown Toronto Up-light Spectrum 2017

The city of Kingston, Ontario, uses LED systems for most of its city streets. Why are certain emission lines still apparent and distinct?

Kingston Ontario Up-light Spectrum

Some American cities..

St-Louis Up-light Spectrum

Chicago used some HUGE wattages just a few years ago, 1000w and 400w HPS were not unusual for downtown. The 2017 sky-glow of Chicago had a strong orange glow. However, away from the city proper it looked much whiter.

Chicago's Sky-Glow

The following 2 spectra where obtained from the same spot on a warm clear night from Schiller Woods, near W. Irving Park and N. Cumberland Ave. First aiming east over Chicago, then west, about 30 minutes apart, the two sky-glow spectra were noticeably different.

Chicago CLear-Night Spectra

How bright is Vegas? It's bright alright and I know exactly what that brightness is made up of; the overcast spectrum appears just slightly different from other cities since Vegas uses plenty of induction-lighting.

Las Vegas Uplight Spectrum

How about a clear night spectrum? The Los Angeles sky-glow acquired from an isolated spot on Griffith Park in 2018:

L.A. Clear Night Spectrum

L.A.'s sky-glow spectrum was not a big surprise. The city had converted its street-lights to LED back in 2014. Hence, on nice and clear nights a blue sky-glow is created.

Evolving Sky-Glow - Updated Spectra

Here are some recent sky-glow spectra, showing the difference with the past, in composites. The first one is over my home. There was no LED-lighting whatsoever in 2008.

Saint-Laurent, Quebec, 2008 vs 2020      Las Vegas, Nevada, 2018 vs 2020

Downtown Montreal, Quebec, 2017 vs 2020      Cornwall, Ontario, 2018 vs 2020

Precise data can be found in the pdf: The New Sky-Glow Spectra.

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