I was looking up the cloud forecast in Astronomy Tools website to see how long before I could image.
I noticed a Sky Quality reading came up, for where I live, and magnitude 21.99 ?
then some more technical stuff I don't understand.
Sky quality Takahue.png
can someone please explain what these technical numbers mean, and also how do they know all this ?
These are just rough estimates of the sky brightness due to natural and artificial sources. The website
attempts to model the sky brightness. They assume natural sources give 22 magnitudes per square arcsecond in the V band (visual green light). This is only a very rough guess, and ignores factors like solar cycle, air glow, weather, moonlight, etc. The natural sky light of 22 mag / arcsec squared corresponds to about 169 micro-candles per square meter.
Light from artificial sources is estimated from satellite photos showing the brightness of artificial lights on earth, and then converted to zenith reflected light based on some model of atmospheric scattering. So at your location the model for artificial light gives 1.53 micro-candles per meter squared. Adding this to the natural light gives the total brightness of 170 micro-candles per square meter or 0.170 milli-candles per square meter.
Your ratio of artificial light to natural sky light is about 0.01 which corresponds to Bortle class 0 on the Bortle scale. This is indicative of very dark skies with almost no light pollution.
If you want to measure the actual night sky brightness at your sire, you can buy a Sky Quality Meter from these folks. This would be much more reliable than the estimates.
Edited by ngc7319_20, 06 February 2023 - 10:21 AM.