Part 1: Where in Oregon is the Night Sky Most Pristine? And, Most Light Polluted?
DarkSky Oregon and volunteers support a network of Sky Quality Meters across the state which continuously record how bright and how dark the night sky is overhead. The data tell us which areas still have pristine night skies, which areas are polluted by artificial light, and which fall in-between.
This map of Oregon shows the locations of our Sky Quality Meters. The size of the yellow plus symbol tells how starry the night sky is at each spot. The largest plus symbols represent nearly pristine night skies – a very rare environment compared to most of the rest of the USA. The smallest plus symbols represent the light polluted sites – around the cities of Central Oregon, the Willamette Valley and Portland.
The next plot shows in detail how dark the night sky is overhead at our measurement locations – this data was used to make the Oregon map above. The darkest – the most pristine – night sky locations are at the bottom of the plot. The most light polluted are at the top of the plot.
Another way to look at the data in the plot is to compare how much brighter the clear (not cloudy) night sky is at each location by comparison to one of the darker, pristine night sky locations.
The rightmost column of this table shows how much brighter each site is, by comparison to the darkest site measured at present, at Crater Lake National Park. The night skies in the cities of Central Oregon sites are about 5x brighter than at Crater Lake. The night skies in Portland are about 20x brighter.
It turns out that clouds at night reflect light pollution downward in cities, causing the night sky to be very bright. And, away from cities, where there is little light pollution, clouds at night are dark because there is no light pollution to reflect back downward, and moreover, the clouds block out the stars, so the night sky measures very dark.
This last table summarizes the brightness of cloudy night skies at our measurement locations. The rightmost column shows that on cloudy nights, the Central Oregon city skies are 20x brighter and Portland skies are up to 300x brighter than the cloudy night skies at pristine night sky sites, a very un-natural situation.
Support the effort to reduce light pollution. Contact us at:
Key Results from the Oregon SQM Network:
