Talk:Arctic Circle

From Wikipedia, the free encyclopedia
Jump to: navigation, search


There's nothing on the article to say how much area the arctic circle encompasses. — Preceding unsigned comment added by (talk) 11:51, 5 June 2011 (UTC)

24 hours daylight/night cycles[edit]

I'm confused with this paragraph.

"The Arctic Circle marks the southern extremity of the polar day (24-hour sunlit day, often referred to as the "midnight sun") and polar night (24-hour sunless night). North of the Arctic Circle, the sun is above the horizon for 24 continuous hours at least once per year and below the horizon for 24 continuous hours at least once per year. On the Arctic Circle those events occur, in principle, exactly once per year, at the June and December solstices, respectively. In fact, because of atmospheric refraction and because the sun appears as a disk and not a point, part of the midnight sun may be seen on the night of the northern summer solstice up to about 50′ (90 km (56 mi)) south of the Arctic Circle; similarly, on the day of the northern winter solstice, part of the sun may be seen up to about 50′ north of the Arctic Circle. That is true at sea level; those limits increase with elevation above sea level although in mountainous regions, there is often no direct view of the true horizon."

Any point directly on the Arctic circle will experience exactly one 24 hour period of daylight/night. But anything North of the arctic circle will never experience an exact 24 hour time period of daylight/night. I have the same confusion with the antarctic circle article.

The articles on the tropic circles seem to be explained better. — Preceding unsigned comment added by Jpaszko (talkcontribs) 20:17, 18 April 2012 (UTC)

"But anything North of the arctic circle will never experience an exact 24 hour time period of daylight/night."

And nowhere in the paragraph says it does. It states "the sun is above the horizon for 24 continuous hours at least once per year". 24 continuous hours can be part of any period longer than 24 hours. The article is accurate as written. Ted (talk) 16:17, 25 April 2017 (UTC)

Me, too. I'm looking for a clear explanation of where on earth people will have sunlight all day and all night (by the clock). Would this be on the northern coast of Alaska? Does anyone live there but a few primitive Eskimos? How long is the period of continuous light? (Yes, I know what the article said about being directly on the circle, or near it. That's not what I'm asking.)
I bet a lot of other people come here looking for answers to the same questions, but go away frustrated. Is there a way to keep all the precise scientific information, while also addressing some of the popular questions? --Uncle Ed (talk) 13:20, 1 May 2017 (UTC)
Everywhere on or within (north of) the arctic circle will experience one period of at least twenty-four hours of continuous daylight each year; on the circle, there will be one period of daylight of exactly twenty-four hours (on the summer solstice); farther north, there will be a period of continuous daylight of at least twenty-four hours (at the summer solstice). If you're asking what parts of Earth's surface geography the circle crosses, you could consult the map located at the upper right corner of this very article; it encircles parts of northern Alaska and Canada, most of Greenland, northern Fennoscandia, and northern Russia. If you're asking specifically about places where people live north of the circle, the section of the article titled "Human habitaton" says that, indeed, roughly four million people live north of the arctic circle (almost all of them in northern Europe); several of the largest cities within the circle are mentioned specifically.-Bryanrutherford0 (talk) 18:46, 1 May 2017 (UTC)
I'd be delighted if some of your answer could find its way into the article (hint, hint). --Uncle Ed (talk) 14:57, 3 May 2017 (UTC)
From the Midnight sun article, "The number of days per year with potential midnight sun increases the farther towards either pole one goes." So using Cambridge Bay and Resolute, Nunavut as examples you can see the first has 24 (clock) hours of sunlight for about 65 days and the second for about 169 days. Template:Ed Poor I'm curious as to why the unnecessary insult towards Eskimos? Be they Eskimos of Alaska or the Inuit of Canada and Greenland the word "primitive" is not one that accurately describes them. CambridgeBayWeather, Uqaqtuq (talk), Sunasuttuq 20:38, 5 May 2017 (UTC) Bad template there Ed Poor CambridgeBayWeather, Uqaqtuq (talk), Sunasuttuq 21:07, 5 May 2017 (UTC)

Epoch 2012[edit]

This is strange and unexplained. — Preceding unsigned comment added by (talk) 16:52, 20 June 2012 (UTC)

I've simplified the text. Bazonka (talk) 17:35, 20 June 2012 (UTC)

June 2016 edits extrapolating the drift to exclude Iceland[edit]

@ As the article points out, the wobble of the Earth's axis is complicated and variable, depending on the motion of the Moon, the movement of water in ocean currents, and numerous other factors. The rate of drift will emphatically not be constant and steady over the next twenty-seven years (read more at Circle of latitude#Movement of the Tropical and Polar circles); this means that your figure based on a linear extrapolation, while technically true, is highly misleading.

Consider this analogy: Today, the stock of Skullcandy (SKUL) has gained roughly 16% in a day's trading. "Should this stock continue to appreciate at approximately 16% per day, by August Skullcandy will have become the world's most valuable publicly traded firm by market capitalization." This is true, but since it is wildly implausible that the stock would continue to gain at that rate for two months (or even for two days), the sentence's implications are extremely misleading.

Now, if you can provide a credible source in which someone who understands this topic well says that the axial tilt is expected to continue to lessen for some decades to come and that the average location of the Circle will move northward at least several hundred meters in that time, then this idea will have a place in the article.-Bryanrutherford0 (talk) 16:03, 8 June 2016 (UTC)

I am not an expert, but based on the formulas presented in Axial tilt, a few decades is easily predictable. It's only when we try to predict thousands or millions of years in advance that it becomes more complicated. --Lasunncty (talk) 01:35, 9 June 2016 (UTC)
Ah! There we are. I hadn't seen that article, but it seems to contain just the sort of sources I was requesting. So, let's see... according to that article, the tenth-order polynomial provided near the end of Axial tilt#Short term gives a good estimate of the mean obliquity for the next several centuries, but it then also clarifies that "periodic motions of the Moon and of Earth in its orbit cause much smaller (9.2 arcseconds) short-period (about 18.6 years) oscillations of the rotation axis of Earth, known as nutation, which add a periodic component to Earth's obliquity" that is not reflected in that polynomial. If this short-term oscillation moves the axis 9.2 seconds back and forth in 18.6 years, then that's roughly one second per year; the linear term in the tenth-order polynomial only gives a rate of .47 seconds per year, meaning that the slower long-term variations will be buried behind the faster short-term variations. If that short-term cycle has an 18.6-year period, then it seems likely that Grímsey might leave and re-enter the Circle repeatedly over the next century, though the longer-term trend over the next several centuries will indeed be for the circle to shift northward and ultimately exclude Grímsey entirely. So, again, the presence of this rapid "nutation" in the axial orientation leads me to feel that the situation is too complicated for the projection of a single tidy date when Grímsey will leave the Arctic Circle; but, we could perhaps expand the existing section on the location of the Arctic Circle to add some of this nuance.-Bryanrutherford0 (talk) 12:41, 9 June 2016 (UTC)

Geography - Length[edit]

I am removing the ridiculous assertion (sourced to BBC) that the Arctic circle is 17662 km in length. This value must be wrong. It defies common sense (and note that the other source provided contradicts it). Why anyone thinks a 10% discrepancy of a geographical distance is reasonable is beyond me. I am explaining why I concluded that the value is wrong: The Earth is an oblate spheroid (approximately). It has an Equatorial radius of 6378.1 km, but it is common knowledge that because of its spin, it bulges around the Equator, so that its Polar Radius (of the circle intersecting both poles) is 6356.8 km, which is 0.33% smaller. This means that circles around the Earth at the poles will be SMALLER than the Equatorial radius. IF the Earth were a perfect sphere, the formula to convert a Latitude to the radius of the circle (of the plane the circle cuts through the Earth with a center on the spin axis somewhere between the center of the Earth and the North Pole is SIMPLE geometry. If, for a point P on the sphere's surface, the Latitude is L and the radius is R and the diameter of the Sphere is D (distance from center of Earth to any point on surface) then cosine(L) = R/D or D*cos(L) = R. This is simple geometry, to repeat myself. Since L = 66° 33' 46.6" and D = between 6378.1 and 6356.8 then R MUST BE between 15939.4 km and 15886.2 km. This isn't anywhere close to 17,000!!! There are two considerations which might (but do not, imho) explain the discrepancy: A. Mountains, valleys, call it surface roughness, which would add distance if you were measuring it using a very small ruler. But I know that the Earth is very very smooth - relatively - for a sphere of its size. You will NOT find an extra 1000 km in cracks, crannies, etc. (well, possibly... if you measured any crack bigger that the van der Waals radius but then the difference between liquids (water) and solids (rock, mud, ice, etc.) would make such a silly exercise futile) Anyway, on reasonable scales, say using a 0.1 km yardstick (meter stick) you are NOT going to find an extra 1000 km. B. There are several more complex/sophisticated models of the Earth's surface, which include both asymmetries and higher order perturbations of ellipsoids, but again these corrections are NOT on the scale of 1000 km. Anyway, unless you can explain why 17662 is correct, despite the facts contradicting it as set out above, please don't revert it. I know this is more or less "original research" but it is simple geometry along with a bit more knowledge of the Earth's shape and smoothness. Most of the information I have invoked is available on Wikipedia. Here's the bit I removed:"The Arctic Circle is roughly 17,662 kilometres (10,975 mi) long.[1]" (talk) 00:00, 2 April 2017 (UTC)

First image needs a date[edit]

The first image has an isotherm drawn on it in red, which means the picture needs to be given a date to clarify when that isotherm was located as drawn. 2601:441:4102:9010:188A:E09:9A5E:7FC2 (talk) 13:26, 9 September 2017 (UTC)

This says it is from 2000, although it was uploaded in 2016. The earliest archive I could find is from 2002. The earliest upload to wikicommons I could find is 2006. --Lasunncty (talk) 07:20, 11 September 2017 (UTC)