Talk:Arctic Circle

fixed polar circle?

Dear all,

I just noticed and tried to correct the dutch version of this page, where it says basically that the polar circle is at 66 30. I added that this approximately as the polar circle shifts every year due to a tilt in the axia. These changes were reverted. I started a discussion on the dutch page as wel as a number of people basically do not believe it and claim the polar circle s fixed. Can we come to some sort of consensus?

Opinnions? — Preceding unsigned comment added by 31.201.235.82 (talk) 17:47, 13 May 2018 (UTC)

What do you want our opinions about? The position you're saying you advanced is correct. If editors on the Dutch wiki aren't convinced, point them to good sources confirming it.-Bryanrutherford0 (talk) 19:06, 13 May 2018 (UTC)

Area?

There's nothing on the article to say how much area the arctic circle encompasses. — Preceding unsigned comment added by 86.23.55.139 (talk) 11:51, 5 June 2011 (UTC)

24 hours daylight/night cycles

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 (talk • contribs) 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. 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

This is strange and unexplained. — Preceding unsigned comment added by 80.189.103.145 (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

@62.232.28.220: 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

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."40.142.182.99 (talk) 00:00, 2 April 2017 (UTC)

References

First image needs a date

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)

There is a date in the image itself, and common knowledge would suggest that a temperature of 10°C is not going to happen in the winter. I am going to delete this template from the image caption. --Craig (t|c) 23:22, 19 January 2020 (UTC)

The question is not about the month, since that is obvious, but rather about the year (or range of years). --Lasunncty (talk) 08:08, 21 January 2020 (UTC)

I suppose that would be interesting and desirable information to have and include (I agree there), but by the time this actually becomes vital information to understand the article the continents will have drifted and the Arctic Circle may have moved. Hence I think there was no point in having the clarification template there for the foreseeable future. --Craig (t|c) 10:57, 21 January 2020 (UTC)

Centre of the sun.

Please see the discussion at wp:Reference desk/Science#A(nta)rctic_Circle Dbfirs 13:09, 20 October 2018 (UTC)

I appreciate that there is only a difference of about 50 arc minutes between the "folk definition" of the sun not being visible at all on the winter solstice, and the astronomical definition dealing with the centre of the sun, but we do need to be precise and not perpetuate a misunderstanding. Midnight sun has a clear explanation of the difference. Also see Burn, Chris. The Polar Night (PDF). The Aurora Research Institute.. Dbfirs 06:32, 21 October 2018 (UTC)

Accuracy of circumference and area.

"The Arctic Circle is roughly 16,000 kilometres (9,900 mi)." "11 December 2018, it runs 66°33′47.4″ north".

Calculated in the WGS84 ellipsoid 66°33′47.4″ north results in 15,984.451633304106 kilometres/kilometers (9,932.277768646173 miles). Used Charles Karney's "Online rhumb line calculations using the RhumbSolve utility" https://geographiclib.sourceforge.io/cgi-bin/RhumbSolve "RhumbSolve is accurate to about 15 nanometers (for the WGS84 ellipsoid)" or 0.000015 of a millimetre/millimeter or 0.00000059 of an inch. In an email to me from Charles Karney: "The accuracy of 15 nanometers that I quote is for paths up to half-way round the earth." "RhumbSolve performs rhumb line calculations". "The path with a constant heading between two points on the ellipsoid at (lat1, lon1) and (lat2, lon2) is called the rhumb line (or loxodrome)". "NOTE: the rhumb line is not the shortest path between two points; that is the geodesic and it is calculated by GeodSolve."

"The area north of the Circle is about 20,000,000 km2 (7,700,000 sq mi).

Calculated in the WGS84 ellipsoid 66°33′47.4″ north results in 21,206,734.733486 km² (8,187,966.056236 sq mi). Used Charles Karney's "Online geodesic polygon calculations using the Planimeter utility" https://geographiclib.sourceforge.io/cgi-bin/Planimeter "Planimeter (version 1.49) calculates the perimeter and area of a polygon whose edges are either geodesics or rhumb lines on the WGS84 ellipsoid." "The result for the area is accurate to about 0.1 m2 per vertex." Sulasgeir (talk) 17:24, 11 December 2018 (UTC)

The theoretical circumference is surprisingly close to 16 000 km, though, in practice, it will probably be slightly longer because the surface doesn't exactly follow the smoothed WGS84 ellipsoid. Should we change 20 million to 21 million square kilometres? Dbfirs 20:53, 11 December 2018 (UTC)

Dbfirs: "The theoretical circumference is surprisingly close to 16 000 km, though, in practice, it will probably be slightly longer because the surface doesn't exactly follow the smoothed WGS84 ellipsoid."

However: Wikipedia "Equator" article: "On Earth, the Equator is about 40,075 km long". "The IUGG standard meridian is, to the nearest millimetre, 40,007.862917 kilometres". Wikipedia "Earth's circumference" article: "Earth's circumference is the distance around the Earth, either around the equator (40,075.017 km[1] or around the poles (40,007.86 km[2])." Wikipedia "Earth" article: "Circumference 40075.017 km equatorial[8] 40007.86 km meridional[11][12]."

Equatorial circumference: Charles Karney's RhumbSolve in both the WGS84 ellipsoid and the GRS80 ellipsoid 40,075.016685578486 km. Meridional circumference, "around the poles": Both Charles Karney's RhumbSolve and GeodSolve https://geographiclib.sourceforge.io/cgi-bin/GeodSolve in the WGS84 ellipsoid 40,007.862917250892 km and for the GRS80 ellipsoid 40,007.862916921828 km.

"40,075 km" and "40,075.017 km" haven't been increased to for example 40,080 km or 40,100 km. "40,007.86 km" and "40,007.862917 kilometres" haven't been increased to for example 40,010 km or 40,100 km.Sulasgeir (talk) 18:07, 12 December 2018 (UTC)

Measuring such distances to millimetre accuracy is pointless except as a mathematical exercise. Dbfirs 23:53, 12 December 2018 (UTC)

More re size- defined perimeter/ defined limit.

" Consequently, the Arctic Circle is currently drifting northwards (shrinking) at a speed of about 15 m (49 ft) per year." This is the last sentence of the lead in section and does not have a reference. This ought to be reworded some how. Such as the angle of Maximum declination of the sun is at this time decreasing at xx milliradians. at the same time the other 3 related circles (Antarctic Circle, Tropic of Cancer, and Tropic of Capricorn are therefore also shifting. Also the 'Climate of Artic' really does not belong here. - Climate should be a totally seperate subject, IMHO. The Article on Tropic of Cancer has a section on Drift - that equally applies to all 4 lines. Wfoj3 (talk) 23:44, 23 May 2021 (UTC)

Main Image Incorrect

I believe the main image "File:Arctic (orthographic projection with highlights).svg" shows the arctic circle to reach much farther south than it should be. 99% of Iceland is south of the arctic circle in reality, yet the image shows much more of it as arctic. ~~~ ThundorLord (talk) 22:55, 11 November 2023 (UTC)

Map

The lead claims the AC is one of the 5 lines that appear on maps of Earth. This is false or misleading. Upon reading it, I went to the Earth wikipedia page. On that page (as of July 13, 2024) there are 5 projections of Earth's (entire) surface (i.e. 'maps'). Exactly NONE of them have "lines". (That article only has the lines on a diagram depicting axial tilt.). Sure, it is true that SOME maps have those (astronomical) lines. But based on my admittedly unscientific sampling, it is far less common than the editors of this piece believe. It's also noteworthy, imho, that the actual astronomical lines (circles) change location from year to year. Yes, even the Equator (if defined as the intersection of the Earth's surface with a plane perpendicular to the Earth's spin axis and exactly midway between the N & S poles)(if it's defined - as it usually is - by geographical standards, then it is fixed by international agreement(s).) 98.17.181.251 (talk) 13:33, 13 July 2024 (UTC)