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  #1  
Old 04-12-2009, 06:10 PM
Stoid Stoid is offline
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How does the North Pole months of light/dark actually work?

I was watching the beginning of "30 Days of Night" which says that Barrow, Alaska has a point each winter where it's night for 30 days. I know or have heard that at the very tip of the pole, it's 6 months of light, 6 months of dark.

In the film, it says "Last Day of Sun" and two guys are standing in the sunlight, doing their thing, then they watch the last sunset for 30 days.

But that doesn't seem right.

How does it work, exactly? Isn't it just ultra-extreme versions of day shortening and lengthening that is experienced everywhere? Meaning, isn't the "last day of sun" maybe 10 minutes of sun? Half an hour? 1 minute? 2 hours? Obviously it can't be 5-8-10 hours of sun on Monday, then 24-7 night for 30 days thereafter!

And the same when it gets light again...isn't there a day when there's just a hint of dawn before it's dark, then a little lighter, a little lighter...

So what are the time periods of light and dark in the days leading up to complete darkness or light? how short do they get before they cease completely?

And is it true about Barrow? 30 days of night? Does it have a corresponding summer month that is 30 days of light? And are there points on the earth between Barrow and the pole, between Barrow and farther south that have 31/29, 32/27, 33/26 etc. until it reaches relatively normal cycles of light and dark or all day/all night? And how can THAT be so...6 on 6 off...same thing, it has to be gradual!

I suddenly HAvE to understand this!
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  #2  
Old 04-12-2009, 06:23 PM
Johanna Johanna is offline
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You guessed it. At extreme latitudes, as winter approaches, the points of sunrise and sunset get closer together--sunrise moves to south by southeast and sunset moves to south by southwest. And the sun's height at noon gets lower and lower toward the horizon, until one day it doesn't clear the horizon. Of course you still get twilight then, as long as the sun's high point at noon is still not too far under the horizon.

Right at the Arctic and Antarctic circles, the sun just grazes the southern horizon at noon on the winter solstice. Call it "low noon."

Slightly south of the Arctic circle, the sun on the winter solstice gets slightly above the horizon at noon, for a brief time.

Slightly north of the circle, the sun doesn't even reach the horizon at noon-- so there is no sunrise. The only sign of noon would be twilight in the south instead of dark night.

Further north toward the pole, even the twilight doesn't occur.

Last edited by Johanna; 04-12-2009 at 06:27 PM..
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  #3  
Old 04-12-2009, 06:30 PM
DSYoungEsq DSYoungEsq is offline
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And since the poles are always either in the shadow, or in the sunlight, they get 6 months of each (more or less, since the sun does have some width), with the days when they switch being the equinoxes.
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Old 04-12-2009, 06:30 PM
Johanna Johanna is offline
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Auto-nitpick, edit time expired-- I should have written that at the Antarctic circle, the sun is in the north at noon.
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  #5  
Old 04-12-2009, 06:37 PM
Napier Napier is offline
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This may help.

You perhaps have noticed that the Sun goes up and comes down, from your point of view wherever you live, but that it also moves sideways somewhat. At either pole, all the daily movement is sideways, with the sun maintaining a constant altitude above the horizon but circling around every 24 hours. Yearly, the altitude isn't constant; it goes above and below the horizon at the vernal and autumnal equinoxes, and it peaks at the summer solstice.
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Old 04-12-2009, 07:48 PM
snailboy snailboy is offline
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Quote:
Originally Posted by Stoid View Post
And is it true about Barrow? 30 days of night? Does it have a corresponding summer month that is 30 days of light? And are there points on the earth between Barrow and the pole, between Barrow and farther south that have 31/29, 32/27, 33/26 etc. until it reaches relatively normal cycles of light and dark or all day/all night? And how can THAT be so...6 on 6 off...same thing, it has to be gradual!
Any place where the sun stays completely below the horizon for 30 days will also be a place where the sun stays completely above the horizon for 30 days. However, there will also be days when the sun only partly sets, so there will be slightly more days of constant daytime than nighttime. Going further south, there will be fewer days of both until there is no longer constant nighttime, and shortly thereafter no constant daytime. Going north, there will be more and more days of both, until it's roughly half a year of daytime and roughly half a year of nighttime at the poles.
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Old 04-12-2009, 07:56 PM
Freddy the Pig Freddy the Pig is offline
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Originally Posted by Stoid View Post
I was watching the beginning of "30 Days of Night" which says that Barrow, Alaska has a point each winter where it's night for 30 days.
Barrow experiences almost 80 days without sunrise every year, between late November and early February.

Here is a table showing how the declination of the Sun changes through the year. Today, April 12, the Sun's declination is about 8.5 degrees north. The Sun won't set today anywhere within 8.5 degrees of the North Pole, and won't rise within 8.5 degrees of the South Pole (ignoring refraction and the finite size of the solar disk.) It's that simple.

Barrow is about 5 degrees north of the Arctic Circle, so at the winter solstice the sun peaks about 5 degrees shy of the southern horizon. This is a fairly deep twilight. Over the ensuing weeks the noontime twilight gradually gets brighter and longer until the Sun rises in early February.

At the poles, the winter-solstice Sun is 23 degrees below the horizon, all day. There is no twlight at all, just night-time blackness. Twilight at the North Pole begins in late January, and gradually brightens until Sunrise around March 18.
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Old 04-12-2009, 08:05 PM
snailboy snailboy is offline
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If my calculations are correct (and I'm not confident they are), there's roughly 26 1/4 more days of daytime than nighttime at the poles. I'd like it if someone could confirm this. I'm not about to attempt to calculate it for other latitudes.

Or maybe 2.66 days. That sounds better.

Last edited by snailboy; 04-12-2009 at 08:10 PM..
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  #9  
Old 04-13-2009, 02:43 AM
Johanna Johanna is offline
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Seen from the poles, the sun goes in a spiral motion, corkscrewing up between the winter and summer solstice, and then corkscrewing down until the winter solstice. It goes around once a day, getting a little higher or a little lower each time around, as if each turn moves the screw perpendicular to the direction of rotation, by the width of one thread.
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Old 04-13-2009, 03:52 AM
flodnak flodnak is offline
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Quote:
Originally Posted by Johanna View Post
Seen from the poles, the sun goes in a spiral motion, corkscrewing up between the winter and summer solstice, and then corkscrewing down until the winter solstice. It goes around once a day, getting a little higher or a little lower each time around, as if each turn moves the screw perpendicular to the direction of rotation, by the width of one thread.
And seen from between the North Pole and the Arctic Circle, after the vernal equinox, the sun will appear to rise and set further and further north each day. When it finally gets to the point that it is setting and rising almost due north, it doesn't disappear but just skims the horizon, and setting and rising are just theoretical concepts. Finally it makes a complete circle, dipping down but not touching the horizon, and that's the so-called Midnight Sun. At midnight, then, the sun is in the north. I stress that because some people seem to assume the sun just stands still in the sky or something. This page has a decent composite image showing what happens.

After the autumnal equinox, the sun appears to rise and set further and further south each day. When it finally gets to the point that it is setting and rising almost due south, it barely peeks up above the horizon. Finally, it just doesn't make it above the horizon at all, and that's the period of winter darkness... though in most inhabited places there's still a faint twilight in the south around noon. For some reason this isn't considered as poetic as the Midnight Sun

My adopted hometown is well south of the Arctic Circle, but even here there are weeks every summer when it never gets dark enough to see more than a handful of the brightest stars. For those of us from more moderate latitudes, it's a bit strange at first to be sitting out in the yard on a warm summer evening, chatting with a friend, only to suddenly look at one's watch and discover it's 1 a.m.
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Old 04-13-2009, 08:09 AM
hibernicus hibernicus is online now
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Quote:
Originally Posted by snailboy View Post
Any place where the sun stays completely below the horizon for 30 days will also be a place where the sun stays completely above the horizon for 30 days.
It's not quite as symmetrical as you imply, because the effect of atmospheric refraction is to raise the apparent elevation of the sun. This means that on some days when the sun would otherwise remain completely below the horizon, the upper limb of the sun will be visible in the south at noon, thus reducing the number of days with no daylight. Similarly, on some days when the sun would partially set at midnight, it remains completely above the horizon.
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Old 04-13-2009, 10:16 AM
Lemur866 Lemur866 is online now
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Also remember that the periods of twilight are very long compared to places on the Equator.

I grew up in Fairbanks, which is below the artic circle. But we get about a month where it never gets dark, even though the sun is below the horizon. The sun slowly sets behind the horizon, travels sideways for a bit, then peeks back up over the horizon and the sky never actually gets dark.

The same phenomenon gives you an extra hour or two of light in the winter. Even though the sun is only technically up for an hour in midwinter, you have a very long period of dawn light and a very long period of dusk light where the sky is light even though the sun isn't up.
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Old 04-13-2009, 12:34 PM
Hari Seldon Hari Seldon is offline
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Ths site: http://www.timeanddate.com/worldcloc...&afl=-11&day=1 shows the sunrise and set times for the month of April in the Norwegian town of Longyearbyen on the remote island of Svalbard, at 78 deg 12' north, which is to say virtually halfway from the arctic circle to the pole. The day length at the beginning of the month they have 15:40 of daylight (and the rest is twilight, no deep night), on April 16, they will have 21:18 and then the sun will rise at 2:06 on April 17 and set 22:08 later on April 18 and then rise 1:23 later and not set again till some time in August.
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  #14  
Old 06-05-2009, 08:17 AM
hysterical_oliver hysterical_oliver is offline
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Endless days/nights

Is there a specific term used for the long days and nights experienced in the north? I am teaching English in Japan and one of my students asked me about it but being from Australia I don't have any experience in the area Any help greatly appreciated!!
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Old 06-05-2009, 09:57 AM
Nars Glinley Nars Glinley is online now
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Cool youtube video of the sun not setting.
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Old 06-05-2009, 10:01 AM
slaphead slaphead is offline
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Originally Posted by hysterical_oliver View Post
Is there a specific term used for the long days and nights experienced in the north?
Don't know about summer but there are plenty of terms for the long dark winter nights - most of them are probably not fit for schoolchildren to hear...
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Old 06-05-2009, 10:06 AM
MikeS MikeS is online now
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Quote:
Originally Posted by hysterical_oliver View Post
Is there a specific term used for the long days and nights experienced in the north?
That would be either "white nights" or "the midnight sun."
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  #18  
Old 06-05-2009, 10:10 AM
Philster Philster is offline
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Remember, the earth is tilted on its axis. Up north, at the very top of the planet, during certain seasons the is towards the sun. You rotate with the planet, but since you are pointing at the sun the whole time, you just rotate under neath it, always receiving light.

Grab a basketball and a compact light source and do a quick mock up to 'get your brain around it'.

Last edited by Philster; 06-05-2009 at 10:11 AM..
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