The Lingering Twilight

[North-Easterly Blast]

It is now getting to the time of the year where northern parts of the UK at least do not get properly dark at night and these areas are actually a lingering twilight.

For it to go properly dark, the sun has to fall 12* below the horizon.

When the sun is between 0* and 4* below, it is Civil Twilight, referred to as the time when the sun is below the horizon but outdoor activities can still be performed with adequate light.

When the sun is 4* to 8* below the horizon, it is Nautical Twilight. This is when objects and the outlines of buildings and trees can be seen, but it is dark for practical purposes, and too dark to see to do outdoor activities. It is actually still possible to read a newspaper outside in this type of twilight.

When the sun is between 8* and 12* below the horizon, the only light that is visible is sky illumination, and the twilight can be seen in the north-western sky around this time. It takes the sun to go 12* below the horizon for the sky to go completely dark and be free from twilight.

Parts of the UK north of the Middlesbrough area are in the 54.5* N zone, so areas north of this see twilight all night at the time of the summer solstice. In the Shetland islands, around 61* North, there is enough twilight to read a newspaper by at 1am in the morning.

[Cymru]

It is now getting to the time of the year where northern parts of the UK at least do not get properly dark at night and these areas are actually a lingering twilight.

For it to go properly dark, the sun has to fall 12* below the horizon.

When the sun is between 0* and 4* below, it is Civil Twilight, referred to as the time when the sun is below the horizon but outdoor activities can still be performed with adequate light.

When the sun is 4* to 8* below the horizon, it is Nautical Twilight. This is when objects and the outlines of buildings and trees can be seen, but it is dark for practical purposes, and too dark to see to do outdoor activities. It is actually still possible to read a newspaper outside in this type of twilight.

When the sun is between 8* and 12* below the horizon, the only light that is visible is sky illumination, and the twilight can be seen in the north-western sky around this time. It takes the sun to go 12* below the horizon for the sky to go completely dark and be free from twilight.

Parts of the UK north of the Middlesbrough area are in the 54.5* N zone, so areas north of this see twilight all night at the time of the summer solstice. In the Shetland islands, around 61* North, there is enough twilight to read a newspaper by at 1am in the morning.

Crikey, I never knew that. I knew, of course, that northern areas of the UK hold on to the light longer than the midlands and southern counties but having enough light to read a newspaper at 1am is something I didn't realise. Amazing.

[Northernlights]

Yes the sunsets are truly amazing at this time of year as they seem to go on forever especially last nights.We are being spoilt with such clear skies for days on end. At midsummer you can see the trace of the sunset all night to the north before dawn at about 2.00 am from here looking north over the Moray Firth, a truly magical time of the year if it is not spoilt by cloud cover.

[Bottesford]

Yeah I love the lingering twilight. 10pm and still enough daylight around to sit out in - fantastic!

I'm not sure if the reason the Sun takes longer to set as you go nearer to the summer solstice due to:

a) the angular movement of it relative to the horizon - meaning that it goes in a more diagonal angle as it sets compared to March/Sept. I know at the equator it can go from a high up blazing Sun to darkness in a very short space of time. The Sun sets vertically so is set enough for total darkness very quickly. Even in Portugal I noticed this - 1 hr before sunset it was still as high as we have it at, say, 6pm in June. But once down, it was gone very quickly indeed.

So does this apply at the winter solstice? Does the Sun take longer to set in December than Sept/March? Or does time of year even affect setting angle?

B ) Just that the Sun never gets low enough to give total darkness

c) Both?

Not sure if this diagram will help explain:

The red line is todays sun path across the sky with each grey line across marking the 1st of each month of the year. Figure of 8 is the Sun's position at that time of day throughout the year.

Looking forward to experiencing true lingering twilight in Iceland this summer (there for solstice!). Sunset 0005, sunrise 0255.

Edited May 1, 2007 by Bottesford

[Rustynailer]

In the Middle of summer you can see the light from the South too, i remember well, watching Haley's comet at midnight and later from here and being amazed that it didn't go fully dark on the horizon, and that wasn't street lights either. Not as strong as the above comments but noticeable all the same.

Regards,

Russ.

[Cookie]

evern with a month half to go till the shortest day its light at 5am hear and dosnet get propelly dark to after 10pm

[johnholmes]

month half to go till the shortest day its light

I think you mean the longest day!

Yes I've sat reading a newspaper on Shetland at midnight, provided one was sat by the window.

[Turnedoutniceagain]

evern with a month half to go till the shortest day its light at 5am hear and dosnet get propelly dark to after 10pm

Translation anyone ?? B)

[Azores Hi]

Translation anyone ?? B)

Aww c'mon. Lets forgive a bit of bad spelling, none of us are perfect and maybe this guy has a problem with spelling such as dyslexia. I for one would applaud anyone who has the guts to post knowing that they may get ridiculed for their spelling. I get the drift of his post and I ag ree. We have increasing lengthening days still to look forward to.

Too much picking on peoples faults could lead us into UKWeather world territory where I for one do not post for fear of being torn apart.

This is a really friendly forum, lets keep it that way.

Edited May 2, 2007 by azores hi

[johnholmes]

nice comment Azores

[summer blizzard]

Evne near Leeds, in June and July we get the 4-8 values, coming back from been out drinkin at 1am, it is shocking how light it still is around the summer solitace, though i have good night vision which may add to what i have just said.

[No Balls Like Snow Balls]

I remember staying overnight in Helsinki a couple of years ago, and it never got dark, i remember sitting outside the hotel at 2AM in daylight thinking i am never going to sleep as it was so light still, i never did sleep all night, i guess it takes a bit of getting used to if it is not what you are acustomed to!!

[Norrance]

I like being able to play 18 holes of golf with the course being quiet as most people don't think of teeing off after 8Pm. When I lived up North we used to regularly finish after 11pm.

Re Cookies post above Lewis is a great place for the light nights. Not quite as light as Shetland but never truly dark in June. B)

[Norrance]

I like being able to play 18 holes of golf with the course being quiet as most people don't think of teeing off after 8Pm. When I lived up North we used to regularly finish after 11pm.

Re Cookies post above Lewis is a great place for the light nights. Not quite as light as Shetland but never truly dark in June. :lol:

That should have said 8 pm. Don't know how I managed to get the smiley in there.

Edited May 2, 2007 by Norrance

[RoisinD]

What an informative thread. Thank you all (well nearly all).

We have regularly driven late Friday evenings from London to Glasgow at this time of year and have always been fascinated by the skyline, especially from midnight on when we hit Cumbria and continue on through Scotland. There is usually very little traffic on the motorways so it is a joy to drive on the roads and still be able to see the outline of the hills etc.

I will now have a better understanding of what is happening.

[Stargazer]

IIRC, the definitions are usually accepted as follows:

Civil Twilight (the old "lighting-up time"): sun 6 degrees below the horizon

Nautical Twilight: 12 degrees

Astronomical Twilight (i.e. when the likes of Stargazer are well and truly satisfied it's properly dark : 18 degrees.

At our summer solstice the sun's declination ("celestial latitude") is approximately +23.5 degrees, i.e. it's overhead at midday at the Tropic of Cancer (23.5 degrees N) and never sets above the Arctic Circle (90-23.5 = 66.5 degrees N). So in northern Shetland (above 60.5 degrees N) the point of civil twilight is never reached, north of Middlesbrough (54.5 degrees N) nautical twilight is never reached and above 48.5 degrees N the sky is never completely dark according to astronomers. Therefore, for the entire British Isles from the Channel Isles (49.2 degrees) northwards it never gets completely dark around June 21.

Here in southern England the period during which we never achieve complete darkness is roughly from the beginning of June to mid July.

As for how long the sun takes to set...strictly speaking, outside the Arctic Circle I think it's the same all year round in any given location (it sets faster the nearer the equator you get). In high latitudes outside the Arctic Circle near the summer solstice it will seem to take longer to set because it never gets truly dark. However, the actual act of setting (if you see what I mean) will always take the same time at a given latitude because the sun is cutting through the horizon at (90-latitude) degrees - for example at 51 degrees N is will always set at 39 degrees to the horizon and therefore appear to set at the same rate since its apparent angular motion in the sky is constant.

Clear as mud?

S.

Edited May 2, 2007 by Stargazer

[Bottesford]

Ah cheers for that Stargazer - does make much more sense now! I'd often been confused as to whether time of year affects sun set/rise speed and it now makes sense that it doesn't.

[davehsug]

This reminds me of a question that I asked a couple of years ago but never had answered!

There is a scientific name for the faint light in the Northern sky at that time of year & I completely forgot what it was. Anyone who can help me this time?

Dave

[Cookie]

Translation anyone ??

Sorry mate Im trying my best

Aww c'mon. Lets forgive a bit of bad spelling, none of us are perfect and maybe this guy has a problem with spelling such as dyslexia. I for one would applaud anyone who has the guts to post knowing that they may get ridiculed for their spelling. I get the drift of his post and I ag ree. We have increasing lengthening days still to look forward to.

Too much picking on peoples faults could lead us into UKWeather world territory where I for one do not post for fear of being torn apart.

This is a really friendly forum, lets keep it that way.

thanks mate

This reminds me of a question that I asked a couple of years ago but never had answered!

There is a scientific name for the faint light in the Northern sky at that time of year & I completely forgot what it was. Anyone who can help me this time?

Dave

I think its the Aurora Borealis

[Gray-Wolf]

This reminds me of a question that I asked a couple of years ago but never had answered!

There is a scientific name for the faint light in the Northern sky at that time of year & I completely forgot what it was. Anyone who can help me this time?

Dave

A 'False Dawn' ? I know some Aurora's, over winter, give us the impression of the summer pre-dawn lightness up this way so maybe that is a false dawn though!

[Noctilucid]

Yeah, ive always noticed that around my birthday (June 21st summer solstice) the sky does always seem, to have a tinge of blue if its clear overhead.

Joe

[tugmistress]

The nights are well and truly short now, i *think* that us up in the north overtake the south in daylight hours about beginning of march as south have longer daylight than the north in winter.

you can't get any further north on the mainland than where i am (well maybe another 3 miles north on dunnet head lol) and the last week has been amazing if i take a walk to the quarry and look out over the atlantic the sun is 'visible' until 10pm ish.

[WBSH]

Yep, days are really getting on the long side now, it's still pretty much light at 9pm now where I live.

Incidently Wunderground.com has Civil twilight as between 0-6 degrees below the horizon, nautical twilight as 6-12 degrees below the horizon and astronomical twilight as 12-18 degrees below the horizon. Meaning complete darkness is where the sun is anything below 18 below.

Twilight

I may be reading it wrong though!