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The lingering twilight

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Here's a thread I post every year

We are now approaching 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.

twilight.gif

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. The glow makes noctilucent clouds visible to the naked eye. These clouds are about 85km up and made up of ice crystals which reflect and refract the sunlight below the horizon. However they are not visible all the time and in some years they are more frequent than at other times.

clouds-noctilucent-bg.jpg

positions.gif

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It comes about so quickly every year and makes going out with my telescopes mostly pointless between May and August (unless it's the Moon or planets I'm looking at). Even now it's not properly dark until 10pm in terms of viewing the sky. We make up for it in the winter when you can be all set-up by 4pm, but then it's so bloody cold it's not appealing either.

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Aye that's the problem with astronomy - the best viewing conditions are always when it's ruddy freezing. Those really clear skies you get between rain bands from a NWly I've often found are the best - or of course northerlies.

All this talk of lingering twilight takes me back to last June in Iceland - now *that* was lingering twilight! More like lingering daylight with it not dark enough for street lamps and only a 2-3 hour interruption in sunlight - amazing it was. Wouldn't be so keen on the other end of the year though!

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Great topic guys makes very interesting reading . Takes me back to my days when i used to work nights in a steel mill, used to go out for a break and see the wonderful twilight in the North in May and June . I love the light nights and longer days and i'm so desperate to dust off my patio table and sit with a few beers on a lovely evening ... dream on !!!!!

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Wow I never knew it never went totally dark during the summer months, you learn something new every day! Interesting read that was.

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Very intresting read mr data

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Well Lerwick from now to about late August won't reach true darkness.

The lingering twilight season has begun for the UK!

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its not quite at that stage here

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My best time of year! The kids are in bed, the noise of daytime activity dies down and there is just me, the twilight and pottering around the garden!

This year I'll have my new fire pit to distract me too!!!

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Sounds lovely GW - I can picture it now down the commune :)

It's only for the six weeks around the solstice that it's possible to read a newspaper outside at 1am here. But it's entertaining walking home from nightclubs at 3.30am at the weekends, and the birds are singing, the sky is blue and the sun's on it's way up :)

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Wonderful it is - really feeling the long evenings now with it well lit to half 8 or so (except today with the heavy storm clouds around). Bit more freedom to be out and about - if it wasn't so wet!

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It was noticeable how the twilight lingered from Manchester on Sunday night. Though the sun set just after 8.30pm, the twilight could still be seen after 10pm.

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Guest Shetland Coastie
Well Lerwick from now to about late August won't reach true darkness.

The lingering twilight season has begun for the UK!

Absolutely! For several weeks either side of mid-summer there is enough light to sit outside and read a newspaper at midnight - if you wanted to!

:)

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It starting to left trouser leg me off.

I keep getting woken up because of how light it is outside in the morning :rolleyes:

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It starting to left trouser leg me off.

I keep getting woken up because of how light it is outside in the morning :lol:

Do you have curtains? Blinds? Are they 'blackout' ones?

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yes and no and no!

just theirs nothing outside my window to block the sunlight is straight out to the sea.

taken from metcheck

current for hs1

Sunrise : 5:34 BST Sunset : 21:11 BST

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11pm tonight still quite bright out!

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below are a few images taken around 11:15 tonight

P6020315.jpg

P6020305.jpg

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As we approach the Equinox, the northern sky is remarkably bright up here throughout the night, as described earlier in the thread.

To illustrate the point, here's a shot taken looking north at 00:30 this morning from outside a certain watering hole in the city centre, that I occasionally frequent...:

post-1217-1213544459_thumb.jpg

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As we approach the Equinox, the northern sky is remarkably bright up here throughout the night, as described earlier in the thread.

To illustrate the point, here's a shot taken looking north at 00:30 this morning from outside a certain watering hole in the city centre, that I occasionally frequent...:

post-1217-1213544459_thumb.jpg

Occasionaly?I thought they named the lounge after you?

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:lol:

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:drunk:

Aye the day you pledged off the drink it took the trained police negotiators three hours to talk the Landlord off that ledge :lol:

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I need to get some snaps up soon. 11:30 at night seems like normal day time

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here we go not the best images I have taken but gives you and idea how light still it is. from 10:30 last night

P6150560.jpg

P6150559.jpg

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here we go not the best images I have taken but gives you and idea how light still it is. from 10:30 last night

P6150560.jpg

P6150559.jpg

are those black things stock? :)

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