Does “Earth Hour” make a difference from a night sky darkness point of view? I have always been skeptical, and do remain somewhat skeptical, but it was interesting to experience two consecutive nights this weekend of which one included “Earth Hour” (29th March 2014). Both images were taken from the same location (give or take 10 metres) 200km south-east of Perth, Western Australia.
The left image shows the all-sky view from 28th March, and the one on he right from the 29th March. The 28th March had some cloud cover, as evident around the periphery of the image. The 29th March was a 2 hour clearing between cloud banks. The cloud on the 28th March likely emphasised the light pollution situation, while the recent rain and weather system may have contributed to the increased green Air Glow on the 29th. From this location is is normal to see significant light pollution from Perth and in recent years from other nearby towns such as Narrogin. A such while the light pollution may be emphasised somewhat by the cloud on the 28th, I am amazed to see such a lack of light pollution in the image from the 29th.
One contributing factor, in addition to Earth Hour, maybe localised cloud on the 29th. It is possible that at the time of the photograph localised cloud was covering and enclosing light pollution from Perth and nearby towns, hence “trapping” the light pollution and limiting it’s visibility from my location. It’s not possible for me to know how much this influenced the situation, but either way the difference in light pollution, the almost absolute lack of it on the 29th, is quite a stark contrast and blatantly obvious.