Posted 30 November 2021 - 06:17 PM
Posted 30 November 2021 - 08:54 PM
Yes, for sure.
Let's say you go from the edge of light red to edge of light yellow: that's 20.91-18.95 = 1.96 magnitudes difference. So the total sky brightness will go down by a factor of 6.08 (2.51 raised to the 1.96 power = 6.08, where 2.51 is the definition of one magnitude). That's a big, big deal. If you're in the middle of light red, then the difference is even bigger.
- George N likes this
Posted 04 December 2021 - 06:43 PM
Around here, yellow is considered a dark site.
- ShaulaB and Kimbo_2112 like this
Posted 08 December 2021 - 11:23 PM
Posted 09 December 2021 - 05:49 AM
This is assuming the yellow zone does not have significant local light pollution, and you’re looking at objects high above the light pollution domes (which will still be visible, and prominent)
That is correct. On the other hand the Original Poster was asking us to compare the light red zone versus dark yellow, and even the worst part of the sky in dark yellow is much darker than the best part of the sky in the light red zone.
This was brought home to me when comparing the sky at my astronomy club's observing field in the exurbs of Boston, MA (USA) versus my country home.
At the club field northwest there's a huge light dome to the southeast from Boston itself and pretty big domes to the north and south from Lowell and Framingham, respectively. Northwest, directly away from Boston, appears strikingly dark, with no obvious light sources at all.
At my country home northwest -- toward Albany, NY -- is startlingly bright, a vast light dome covering a whole quadrant of the sky. But guess what? Measurements with sky quality meter and camera confirm that the very worst part of the sky there, 15 degrees directly above Albany, is darker than the zenith at my club's field. And my astronomy club is in the orange zone, not the red zone.
So the only reason that the northwestern sky at the club site appears dark is because the rest of the sky is so bright. Or, looking at it a different way, northwest at my country home appears bright only because the rest of the sky is darker than most suburbanites can imagine -- though still very, very far from being truly dark.
Put yet another way, the difference between deep-sky observing in the dark yellow zone and the light red zone is bigger than words can properly convey.
- George N and DaveL like this
Posted 12 December 2021 - 09:30 AM
Hello fellow darker sky seekers. Newbie here.
So, the light pollution rating at my home per the "Good To Stargaze" app, is an 8.6. The rating at another spot I can use about 1/2 hour away is rated at 5.6. Will there be a significant difference in my viewing experiences at each location? The "lightpollutionmap.info" shows white at home, and border yellow/red at my remote location. I plan on trying the remote location at my first opportunity either way.
Posted 12 December 2021 - 12:29 PM
Posted 14 December 2021 - 11:12 PM
Personally, if you’re only talking about half and hour’s drive, I’d think you were far more likely to be impacted by local things like presence of street lights or nearby houses, than general light pollution.
I disagree, in half an hour I can drive from my house (red zone, SQM = 19's) to a site in the green zone (SQM=21.2-21.4). Local lights do matter for glare, but a half hour drive matters a lot if you are on the edge of a city. If you are driving, use your car to block local lights if they are in one direction.
Posted 15 December 2021 - 08:08 AM
A half hour drive matters a lot if you are on the edge of a city.
Indeed it does. And it matters even more if you're near the center of a city -- at least a concentrated city of the type that's the norm in most of the world.
Mind you, the person who posted this is from Cumbria, which first of all has no cities worthy of the name and secondly has no roads where you can drive a whole lot faster than 40 km per hour.
Posted 16 December 2021 - 02:42 AM
40kmh? Do you think I'm Lewis Hamilton?!
You're both quite right!