Telling the Difference between light polution and hazy skies?

[Manok101]

Sometimes the viewing looks ok, even though I can tell there are hazy clouds in the sky. Sometimes I can't see a darn thing, not even clouds in the sky. My question is how do I tell what's the haze and whats the LP?

[umadog]

I think the two are rather tightly linked. The reason the light pollution is a problem is because light scatters off particles and molecules in the air. On a hazy night there's more scatter and the LP is worse. If we didn't have an atmosphere, there'd be no sky-glow at all. I think it's a fair bet that your local light spillage is similar every night (unless there're things like local stadia which turn on the lights only rarely) so any variation you see is probably due to haze and dust, etc.

[laser_jock99]

I think the two are rather tightly linked. The reason the light pollution is a problem is because light scatters off particles and molecules in the air.

Absolutely correct- more haze in the atmosphere = more visible light pollution. Taken to it's extremes- on a cloudy night you'll just see the under lit bottom of the cloud layer. If it's ultra clear (very rare) then there is less for the upward light spill to scatter off.

[Tim]

As an indicator, the metoffice give a "Visibility" forecast, and also a recorded figure for the hours just passed.

The higher the KM figure for visibility, the better the transparency will be, and the less the LP will be noticeable. Low vis figures indicate moisture and particles in the air.

You can gauge the conditions somewhat by observing stars with your naked eye. Start at the horizon and work your way up to where they stop twinkling. On a good night even low down stars will be clearly visible and not too sparkly. On a bad night even stars right overhead will be twinkling all over the place. On such a night it can be hard to track down fainter objects, and pictures taken will tend to have bloaty stars and loss of detail.

Usually cold clear nights with a patch of high pressure overhead will produce the best conditions, but not always.

It has to be said that in the UK, conditions are very rarely perfect, but even when they are rubbish, there is usually something worth observing.

Hope that helps a bit.

Tim