The Lingering Twilight

[Weather-history]

The new season is about to start in the Northern Isles in only a few days time!~

We are now at the time of the year where it never goes completely dark at night and the UK night is actually a lingering twilight. For twilight to end, the sun has to be 18 degrees below the horizon.

Date when Astronomical twilight is not reached for these locations

Lerwick: 21st April

Aberdeen: 1st of May

Belfast: 10th May

Manchester: 15th May

London: 22nd May

Plymouth: 30th May

At the solstice, the sun skims across the horizon at the latitude of the Arctic Circle (66 2/3 degrees north). To calculate the maximum angle that the sun dips below the horizon around the solstice, you simply deduct the latitude of your location from the latitude of the Arctic Circle. eg Manchester's latitude ~ 53 degrees N therefore maximum angle that sun is below the horizon is (latitude of Arctic Circle - latitude of location) = 13 degrees below the horizon. Manchester is within the 18 degrees limit and indeed no location in the UK is outside this limit. The critical latitude is 48 degrees N, so places in the Med do not experience the lingering twilight.

Civil twilight: When the sun is between 0 and 6 degrees below the horizon

Nautical twilight: When the sun is between 6-12 degrees below the horizon.

Astronomical twilight: When the sun is between 12-18 degrees below the horizon.

Only when the sun is 18 degrees and more below the horizon is there true darkness.

The lingering twilight can be seen to the north between midnight and 1 o'clock as a glow near the horizon. The brightness of the glow depends on how far north you are. In the Channel Islands, the glow is very weak but in the Shetlands it is bright.

Midnight looking due north, 12th June 2009

The most amazing incidence of the lingering twilight was July 1908 after the Tunguska event when it was remarkably bright even at 1am

Here is a remarkable photo. Remember this was before BST, so to gauge it add 1hr to the time stated i.e see it as (11.05pm BST)

[Gray-Wolf]

Seeing as we're only 10 days away from our glorious 'lingering twilight' period do folk feel that the low solar driven 'Atlantic blocking' will bring us better sightings of noctilunimescent clouds or will low solar nobble their formation?

[frogesque]

Seeing as we're only 10 days away from our glorious 'lingering twilight' period do folk feel that the low solar driven 'Atlantic blocking' will bring us better sightings of noctilunimescent clouds or will low solar nobble their formation?

Peeked out last night before going to bed and the sky conditions looked perfect. No sign of NLCs but they could apear at any time from now Be interesting to see if the eruption in Iceland has any effect on NLcs due to sulphur or ash at high levels. Thinking possible different shades or colours other than the normal electric blue.

[Guest]

I find this site useful as it gives sunrise times and twilight times too:

http://www.timeanddate.com/worldclock/sunrise.html

Click your rough location and then on the far right drop down menu ("Columns") choose twilight...