Bright nights?

[Manok101]

Every now and then the sky looks too bright at night, and it doesn't seem to be related to the clouds, or moon, and I was wondering what might cause this? Is it possibly clouds I can't see that cause it?

[LukeSkywatcher]

When you say too bright, what colour is it?.

[cantab]

In summer it's because the Sun never gets low enough below the horizon for the sky to be truly dark; even at midnight it's still twilight conditions.

I've also heard it's possible clouds to darken the sky. Specifically, if there's a city some distance away then when there are clouds over that city but not over you the clouds will block the light pollution from the city and darken the sky.

[Hals]

Definitely due to the Sun being not far below the northern horizon...however you'll often get a lot of light scattering which makes it seem even worse.

Depending on the state of the Sun and your latitude you may see aurorae and quite often noctillucent clouds (Nocti's have nowt to do with the Sun directly though !).

This time of year I'll often concentrate on observing doubles and planetary nebulae as both can stand higher magnification and this effectively darkens the sky as viewed through your eyepiece.

However saying that there's still great fun in sweeping the milky way areas around Cygnus with binoculars.

[LukeSkywatcher]

Definitely due to the Sun being not far below the northern horizon.

Dont you mean the Western horizon?. I am in Dublin, it is 10:30pm and honestly i could easily read a book outside with no problem.

Thats why my scopes are tucked away til at least the end of August, if not the end of Sept.

It is really only dark (and not real real dark) here at about midnight and the sky starts to brighten between 2-3am.

[Hals]

Ha ! I guess it's north western right now but I meant it in general terms Luke.

[LukeSkywatcher]

Ha ! I guess it's north western right now but I meant it in general terms Luke.

Yeah i was being a bit pedantic(sp?).

Dont mind me................i blame the bright nights,getting bright between 2-3am and the damn dawn chorus for my lack of sleep.

[Bart]

I have pretty good dark skies, but sometimes my western sky, which is the least best direction for light pollution, looks worse than normal becasue the clouds are sitting low and the LP looks worse (easier to illuminate) than when there is less clouds/higher clouds. Maybe your situation?

Bart

[LukeSkywatcher]

I never observe westward because my house gets in the way.

[ollypenrice]

Down in southern France we get a minimum of about 4 hours full astronomical darkness even around the 21st of June. If it isn't the summer nights that you mean then it can either be moonlight or cloud. Now cloud is an odd one. An earlier post says that cloud over a city can trap its light. This may be true but my own experience is actually just the reverse. I live at a very dark site and when there sky is cloudless and dry down to the horizon the horizons are far darker than when there is a damper atmosphere or a little low cloud. The low cloud or moisture scatters the distant lights of the cities about 80 miles away and lifts it higher above the horizon. Haze makes the sky lighter and makes any light pollution worse in my view. The clearer the sky the darker it is, unless you are in a real pea souper and then you're done for anyway!

Olly

[Manok101]

Its kind of like, a dimmer version of the moon's light pollution, not the cities, I can tell the difference usually, but lately there has been no moon. thanks for all of our answers.

[Avo]

The other morning, 01:30 ish.

No stars........................

[JamesF]

So we're clear what I'm talking about, let's say you're standing outside around midsummer in the northern hemisphere, facing south. Take a flask; you're going to be there a while... The sun rises behind your left shoulder to the north-east, travels across the sky until noon when it's high, but to the south of you, and then drops back down over your right shoulder to the north-west, passing around "behind" the earth to the north before coming up again in the north-east. Unless you're in the tropics the sun never travels around the earth "under your feet", just as it never goes directly above your head.

The Earth is currently inclined at about 23.5 degrees from the vertical, northern hemisphere towards the sun during the day. After scribbling on a bit of paper I think I'm correct in saying that as the sun passes in front of you to the south then at its highest it will reach an altitude of ( 90 - latitude + 23.5 ), so 62.5 degrees above the horizon for me. At night as it passes behind your head and the planet to the north it will be at most ( 90 - latitude - 23.5 ) below the horizon, so 15.5 degrees for me. As "astronomical darkness" is defined as "when the sun is 18 degrees or more below the horizon" it's not going to be that dark here. And I'm fairly well south for the UK. If you're at 59N in the Orkneys the sun won't drop more than seven degrees below the northern horizon and I imagine it's pretty light all the time. Olly on the other hand, at a mere 44N, has the sun descend to 22.5 degrees below the horizon and so it's "properly" dark for a reasonable time still.

Cloud and moisture in the air seems to be quite complex in its effects. Sometimes here the clouds can turn night absolutely pitch black so you can't even see your hand in front of your face. At other times they reflect and diffuse light around so much that it's like twilight when it should be dark. It may depend on the altitude of clouds (it can be astonishingly dark inside a cloud) and whether they're light and fluffy or dark thunderheads. I seem to suffer most with LP from Taunton to the south-east when there's "just enough" moisture in the air without it necessarily being particularly cloudy as that seems to diffuse the light most. When there's more solid white cloud it seems to reflect the light, but "contain" it more.

James

[S.A.M]

^{Last night while driving back from Wiltshire AS monthly meeting (around 10:15), I could see the roads clearly without using driving lights (if I wanted to), the sky was still that bright and there was an orange glow to the NW/N direction.}

[Manok101]

I remember once when we had a snow/fog storm it was bright enough because of the city lights nearby that it looked like daylight outside. I tried and tried but at the time I was missing my ipod so couldn't take a picture of it.

[rwilkey]

Up in Thurso and the Shetlands a couple of years ago, I found it strange that it was still light at midnight, very stange for a southerner anyway!

[ollypenrice]

Guests doing widefield imaging last night had some streaks of fine high cloud drift over some of their images. It is very obvious in these images that the cloud brightens the affected part of the picture. Interesting.

Olly

[sologuitarist61]

Even down oin the south the skies are bright this time of the year. On the last sunny day we had (day before last) I waited until midnight to see what the sky would be like and in the west/north west the sky was still very bright following the sunset earlier, so I gave up and went to bed.