What is the size of the Arctic Circle What is the diameter or length width?

Answer 1

Length or circumference of the Arctic / Antarctic Circle.

This depends on the time, date, and whether the calculations are made using True or Mean obliquity of the ecliptic.

All at UT Hours 00 Minutes 00 Seconds 00.000:

1 January 2016, calculated in True obliquity: Latitude WGS84 66° 33' 55.782" North/South, length 15982.955 kilometres/kilometers or 9931.348 international miles or 8630.105 international nautical miles.

1 January 2016, calculated in Mean obliquity: 66° 33' 46.041" N/S, length 15984.694 km or 9932.429 international miles or 8631.044 international nautical miles.

1 July 2016, calculated in True obliquity: 66° 33' 55.842" N/S, length 15982.944 km or 9931.341 international miles or 8630.099 international nautical miles.

1 July 2016, calculated in Mean obliquity: 66° 33' 46.274" N/S, length 15984.653 km or 9932.403 international miles or 8631.022 international nautical miles.

1 January 2017, calculated in True obliquity: 66° 33' 55.556" N/S, length 15982.995 km or 9931.373 international miles or 8630.127 international nautical miles.

1 January 2017, calculated in Mean obliquity: 66° 33' 46.510" N/S, length 15984.611 km or 9932.377 international miles or 8630.999 international nautical miles.

To calculate the latitudes I used the PHP Science Labs website, Obliquity of the Ecliptic and Nutation in Obliquity calculator (for True using the IAU 2000B series), and for the distances Charles Karney's RhumbSolve online rhumb line calculator.

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."

True obliquity of the ecliptic is used to calculate the latitudes of the Arctic Circle, sent to me from the National Land Survey of Finland, the Finnish Geodetic Institute, calculated the latitudes sent to me, for every ten days, for the years 2000-2049. The GIT Barents website (which is now the Aboriginal Mapping Network, and has been totally altered), had on it the following: "the circle has in 2006 passed the peak of the motion wave: Until the year 2015 the Arctic Circle will travel again 700 metres to the north, and after that it will continue to the south about 450 metres during the following nine years. Depending on the phase of the motion, the Arctic Circle can move over three metres a day and over 100 metres a year!"

This was obviously also calculated using True obliquity of the ecliptic.

In my opinion true obliquity of the ecliptic should be used. Since true obliquity is the actual, hence "true". Mean obliquity of the ecliptic is only obviously the mean, and is in my opinion, just for the convenience of humans. Since when for example using mean obliquity of the ecliptic for the Arctic Circle, it supposedly will only move north at an equal, regular rate, for about the next 10,000 years. Which makes for far easier calculations of the latitudes. Mean is just that, only the mean movement. In my opinion, the Arctic Circle is actually moving mostly north but sometimes south, for about the next 10,000 years, and it moves in a seemingly random, unpredictable manner (true obliquity of the ecliptic). Of course this would mean, that Antarctic Circle is moving mostly south, but sometimes north, for about the next 10,000 years. The Swedish National Land Survey or Landmäteriet website has an Arctic Circle latitude calculator, that calculates in both mean and true obliquity of the ecliptic. However it only gives two latitudes for each year, one for mean obliquity, the other for true obliquity. For 2016, Mean obliquity 66° 33' 46.07" N, True obliquity 66° 33' 54.92" N. Using the PHP Science Labs website, Obliquity of the Ecliptic and Nutation in Obliquity calculator, True obliquity 66° 33' 54.92" N is at least closest to 3 March, and Mean obliquity 66° 33' 46.07" N is closest to 24 January.

Extract from a National Land Survey of Finland document:

Latitude and movement of the Arctic Circle

Since [year,month,day,h,m,s]: 2000 1 1 0 0 0.

Until [year,month,day,h,m,s]: 2050 1 1 0 0 0.

Step [days]: 10.00 Longitude: 30.00

Date UT B.Y. Latitude Days Movement from 2000 1 1 0 0 .00

Y M D H Min Sec [m]

2015 12 28 0 0 .00 2015.99 66 33 55.903 5840.00 359.0

2016 1 7 0 0 .00 2016.02 66 33 55.863 5850.00 357.7

2016 1 17 0 0 .00 2016.04 66 33 55.618 5860.00 350.1

2016 1 27 0 0 .00 2016.07 66 33 55.433 5870.00 344.4

2016 2 6 0 0 .00 2016.10 66 33 55.359 5880.00 342.1

2016 2 16 0 0 .00 2016.13 66 33 55.137 5890.00 335.2

2016 2 26 0 0 .00 2016.15 66 33 54.852 5900.00 326.4

2016 3 7 0 0 .00 2016.18 66 33 54.793 5910.00 324.6

2016 3 17 0 0 .00 2016.21 66 33 54.816 5920.00 325.3

2016 3 27 0 0 .00 2016.24 66 33 54.756 5930.00 323.4

2016 4 6 0 0 .00 2016.26 66 33 54.754 5940.00 323.4

2016 4 16 0 0 .00 2016.29 66 33 54.967 5950.00 330.0

2016 4 26 0 0 .00 2016.32 66 33 55.211 5960.00 337.5

2016 5 6 0 0 .00 2016.35 66 33 55.299 5970.00 340.3

2016 5 16 0 0 .00 2016.37 66 33 55.447 5980.00 344.9

2016 5 26 0 0 .00 2016.40 66 33 55.736 5990.00 353.8

2016 6 5 0 0 .00 2016.43 66 33 55.863 6000.00 357.7

2016 6 15 0 0 .00 2016.45 66 33 55.801 6010.00 355.8

2016 6 25 0 0 .00 2016.48 66 33 55.821 6020.00 356.4

2016 7 5 0 0 .00 2016.51 66 33 55.855 6030.00 357.5

2016 7 15 0 0 .00 2016.54 66 33 55.689 6040.00 352.3

2016 7 25 0 0 .00 2016.56 66 33 55.419 6050.00 344.0

2016 8 4 0 0 .00 2016.59 66 33 55.283 6060.00 339.7

2016 8 14 0 0 .00 2016.62 66 33 55.180 6070.00 336.6

2016 8 24 0 0 .00 2016.65 66 33 54.909 6080.00 328.2

2016 9 3 0 0 .00 2016.67 66 33 54.682 6090.00 321.1

2016 9 13 0 0 .00 2016.70 66 33 54.693 6100.00 321.5

2016 9 23 0 0 .00 2016.73 66 33 54.684 6110.00 321.2

2016 10 3 0 0 .00 2016.76 66 33 54.590 6120.00 318.3

2016 10 13 0 0 .00 2016.78 66 33 54.660 6130.00 320.4

2016 10 23 0 0 .00 2016.81 66 33 54.889 6140.00 327.5

2016 11 2 0 0 .00 2016.84 66 33 55.064 6150.00 333.0

2016 11 12 0 0 .00 2016.87 66 33 55.129 6160.00 335.0

2016 11 22 0 0 .00 2016.89 66 33 55.328 6170.00 341.1

2016 12 2 0 0 .00 2016.92 66 33 55.592 6180.00 349.3

2016 12 12 0 0 .00 2016.95 66 33 55.611 6190.00 349.9

2016 12 22 0 0 .00 2016.97 66 33 55.529 6200.00 347.4

2017 1 1 0 0 .00 2017.00 66 33 55.559 6210.00 348.3