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The Lingering Twilight And Noctilucent Clouds


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Posted
  • Location: Irlam
  • Location: Irlam

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

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Posted
  • Location: Berlin, Germany
  • Weather Preferences: Ample sunshine; Hot weather; Mixed winters with cold and mild spells
  • Location: Berlin, Germany

Ahh the lingering twilight - my favourite time of year (even though it makes astronomy even more light polluted than normal!). Almost always light or at least glowing in the distance. Looks like it'll be about mid May it begins here (with a late July/early August finish I would have thought...)

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Posted
  • Location: Canterbury, Kent
  • Location: Canterbury, Kent

My latitude is 51N so the sun will therefore never get below 15 degrees below the horizon during the summer soliste. Although this is not always visible especially during cloudy, wet nights.

The latest I have seen noctilucent clouds in the faint twilight was last summer around mid-summer at between 11:15pm to 11:20pm. I wish I had a camera with me then! and the earliest I saw the morning twilight was at 3:22am 26th of June last year... I remember noticing a faint light through the breaking clouds of the eastern horizon at 3:22am and by 3:39am I reported that the light started to spread to most of the sky and I started to hear birds singing the dawn chorus. It suprised me how early It got light around mid-summer and this was a cloudy morning as well!

When I was up in Iceland last July I could remember seeing the sun just above the horizon at 11:15pm and then sitting outside my hotel the same "night" at 11:30pm with little or no need for artificial light. Surreal but a great experience! I'm not even sure it reached civil twilight (0-6 degrees?) there!

WBSH

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Posted
  • Location: Worcestershire
  • Location: Worcestershire

interesting Read Mr data :)

Love those warm summer nights, where you could get up at 1am look out your window (west) and see the bluey glow on the horizon, ahhh :o

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Posted
  • Location: Swansea (West)
  • Weather Preferences: Snow, Thunderstorms, Hot Summer days
  • Location: Swansea (West)

Its quite weird in summer, at around 3am, as you can see a silhouette of the mountains to the north, with the brightning sky to the north.

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Posted
  • Location: Atherstone on Stour: 160ft asl
  • Location: Atherstone on Stour: 160ft asl

As a family, we're lucky enough to have use of a friend's holiday cottage in the Kyle of Tongue (The flat bit on the North of Scotland - Caithness). I try & time a visit with the Sum' Solstice as the light is quite unbelievable.

With the aid of a couple of coats it's quite possible to sit outside at midnight & read the paper. In fact, the local golf club have a midnight trophy that involves tee-ing off @ 10pm & playing thru' the night. Suns up again at 2am-ish.

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Posted
  • Location: Hanley, Stoke-on-trent
  • Location: Hanley, Stoke-on-trent

Isn't there a name for this twilight, or at least the never quite complete darkness? I remember hearing it years ago but have forgotten. Anyone know it?

Dave

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Posted
  • Location: Berlin, Germany
  • Weather Preferences: Ample sunshine; Hot weather; Mixed winters with cold and mild spells
  • Location: Berlin, Germany
Isn't there a name for this twilight, or at least the never quite complete darkness? I remember hearing it years ago but have forgotten. Anyone know it?

Dave

Astronomical twilight - as mentioned in first post :D

Should be able to really feel the day length tonight with the clear skies above me. Been mostly cloudy for quite a while so tonight will feel like a lovely long evening.

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"Isn't there a name for this twilight, or at least the never quite complete darkness? I remember hearing it years ago but have forgotten. Anyone know it?"

By far the best word for it is "Gloaming".

Made famous by Sir Harry Lauder, with his song "Roaming in the Gloaming".

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Posted
  • Location: Hanley, Stoke-on-trent
  • Location: Hanley, Stoke-on-trent

Thanks for the replies but I was thinking of a specific word to describe it. I know I heard it years ago but I'm getting on a bit now!

Dave

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  • 3 weeks later...
Posted
  • Location: Swansea (West)
  • Weather Preferences: Snow, Thunderstorms, Hot Summer days
  • Location: Swansea (West)

http://aim.hamptonu.edu/

The AIM satellite mission will explore Polar Mesospheric Clouds (PMCs), also called noctilucent clouds, to find out why they form and why they are changing.

http://aim.hamptonu.edu/outreach/index.html, mission summary page, also shows the instruments used (click next on for-mentioned page)

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  • 3 weeks later...
Posted
  • Location: Swansea (West)
  • Weather Preferences: Snow, Thunderstorms, Hot Summer days
  • Location: Swansea (West)

woke around 3am this morning and the sky was an orangy colour to the northern horizon.

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Posted
  • Location: Leicester City Centre (Home) Ashby-De-La-Zouch (Work)
  • Location: Leicester City Centre (Home) Ashby-De-La-Zouch (Work)

It begins to get light about 04:00 here, as I can't see the horizon I'm not sure what time the sun begins to come up but it's almost like daylight come 05:00.

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Posted
  • Location: Stanley, County Durham.
  • Weather Preferences: Anything Extreme!
  • Location: Stanley, County Durham.

Just got an e-mail from SpaceWeather.com about this:

STRANGE CLOUDS; Last night, sky watchers in Northern Ireland witnessed a vivid display of electric-blue noctilucent clouds. Also known as "NLCs," these clouds float through the outer reaches of Earth's atmosphere at the very edge of space. They are most often seen from far-northern places such as Scandinavia or Canada, but in recent years they have been spotted as far south as Colorado and Utah. Last night's display marks the beginning of the 2006 noctilucent cloud season. Visit http://spaceweather.com for observing tips and a gallery of recent sightings.

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i noticed on friday as i stayed up till about 03:30am never seemed to go dark once. there was always a visable light in the sky from sunset to sunrise didnt take any pics as batteries were on charge wanted to time lapse it aswell

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Posted
  • Location: 4 miles north of Durham City
  • Location: 4 miles north of Durham City
this is what I bloody saw the night I went out without my memory card in my camera....Friday night it was.

Yup, it scared the sh*t out of me.

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Posted
  • Location: Douglas, Isle of Man
  • Location: Douglas, Isle of Man

It showed up very well on www.manxradio.com/webcam.aspx baycam, but I didn't think to capture the image :)

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Posted
  • Location: Sth Staffs/Shrops 105m/345' & NW Snowdonia 219m/719'
  • Location: Sth Staffs/Shrops 105m/345' & NW Snowdonia 219m/719'

A shed load more of pictures (3 page thread) of the recent noctilucent clouds from the guys in Northern Ireland who posted on spaceweather.com

East Antrim Astronomical Society Forum

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Posted
  • Location: Canterbury, Kent
  • Location: Canterbury, Kent
000_0140.jpg

I saw a horizon like that last June past 11pm.

The mostly clear conditions are great for twilight watching at the moment, although i've yet to see the same sort of twilight at 11:40pm as in the pic of Mr.Data. I'm probably too far south for that.

WBSH

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  • 2 weeks later...
Posted
  • Location: Sth Staffs/Shrops 105m/345' & NW Snowdonia 219m/719'
  • Location: Sth Staffs/Shrops 105m/345' & NW Snowdonia 219m/719'

Some very nice Noctilucent Clouds visible across the UK last night.

http://spaceweather3.com/nlcs/gallery2006_page1.htm

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