Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: evan_au on 26/10/2016 08:37:43

Title: How can we restore dark skies?
Post by: evan_au on 26/10/2016 08:37:43

This week's podcast asked "How can we restore dark skies?".

I was interested in the comment on the podcast that one town had improved its skies by replacing old sodium-vapor steet lamps.

The rural town of Coonabarabran in Australia hosts the nearby Anglo-Australian telescope. Dark skies are a goal for this town. When I was last there, they pointed out that they used (downwards-pointing) sodium-vapor lamps because they were so astronomer-friendly! An incandescent light causes sky glow at all visible wavelengths, and a mercury-vapor lamp causes sky glow at many wavelengths. A sodium-vapor lamp emits almost all its light at just two closely-spaced yellow wavelengths. Because this yellow light has zero red shift, it is easy for astronomers to ignore it.

I heard of a Nordic town which had a goal that street lighting should become carbon-neutral. So they mounted solar panels and windmills on the light poles. They also installed motion sensors, so the lamp only illuminated when a pedestrian or vehicle approached, and faded out after they left. This would greatly reduce the amount of unnecessary light on the streets at night.  Whether it would bring out unsavory characters to lurk unmoving in the shadows would be an interesting question - or whether their inevitable movement would highlight their presence to neighbors...

Title: Re: How can we restore dark skies?
Post by: Colin2B on 26/10/2016 08:55:19

In the U.K. you have have to move well away from towns to watch meteor showers etc.
I've come across local councils using the sensor approach, but now noticed a few using led where the spectrum won't be Astro friendly and there will be less inclination to spend money on switches.

Title: Re: How can we restore dark skies?
Post by: mrsmith2211 on 27/10/2016 23:42:47

I remember as a kid stars from horizon to horizon, now there is a 15% dull zone at the bottom of the horizon. No streetlights, but it is nice to see the milky way when clear. Particulate matter my guess.

Title: Re: How can we restore dark skies?
Post by: alancalverd on 28/10/2016 04:55:04

The evidence that street lighting reduces crime is actually very weak, and it is quite clear that lighting motorways increases scatter glare and thus reduces hazard conspicuity in fog. Far better to switch the lights off altogether. City streets are adequately lit by shop windows.