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User:DMBFFF/Dekadays beginning from winter solstice

From Fiction and Fictional Settings Wiki

links to and content forked from Wikipedia

w:December solstice
w:Winter solstice
w:Season#Astronomical

Astronomical

Template:Longitem
event w:equinox w:solstice w:equinox w:solstice
month March June September December
year
day time day time day time day time
2015 20 22:45 21 16:38 23 08:20 22 04:48
2016 20 04:31 20 22:35 22 14:21 21 10:45
2017 20 10:29 21 04:25 22 20:02 21 16:29
2018 20 16:15 21 10:07 23 01:54 21 22:22
2019 20 21:58 21 15:54 23 07:50 22 04:19
2020 20 03:50 20 21:43 22 13:31 21 10:03
2021 20 09:37 21 03:32 22 19:21 21 15:59
2022 20 15:33 21 09:14 23 01:04 21 21:48
2023 20 21:25 21 14:58 23 06:50 22 03:28
2024 20 03:07 20 20:51 22 12:44 21 09:20
2025 20 09:02 21 02:42 22 18:20 21 15:03

Astronomical timing as the basis for designating the temperate seasons dates back at least to the w:Julian calendar used by the ancient Romans. It continues to be used on many modern Gregorian calendars worldwide, although some countries like Australia, New Zealand, Pakistan and Russia prefer to use meteorological reckoning. The precise timing of the seasons is determined by the exact times of transit of the sun over the tropics of Cancer and Capricorn for the w:solstices and the times of the sun's transit over the equator for the w:equinoxes, or a traditional date close to these times.[1]

The following diagram shows the relation between the line of solstice and the line of w:apsides of Earth's elliptical orbit. The orbital ellipse (with eccentricity exaggerated for effect) goes through each of the six Earth images, which are sequentially the perihelion (w:apsis#Earth's perihelion and aphelion—periapsis—nearest point to the sun) on anywhere from 2 January to 5 January, the point of March equinox on 19, 20 or 21 March, the point of June solstice on 20 or 21 June, the aphelion (w:apsis#Earth's perihelion and aphelion)—apoapsis—farthest point from the sun) on anywhere from 4 July to 7 July, the September equinox on 22 or 23 September, and the December solstice on 21 or 22 December.

Illustration of seasonal distances from Earth to the Sun
Note: Distances are exaggerated and not to scale

These "astronomical" seasons are not of equal length, because of the (elliptical nature) (w:ellipse of the orbit of the Earth, as discovered by w:Johannes Kepler. From the March equinox it currently takes 92.75 days until the June solstice, then 93.65 days until the September equinox, 89.85 days until the December solstice and finally 88.99 days until the March equinox.

Variation due to calendar misalignment

The times of the equinoxes and solstices are not fixed with respect to the modern Gregorian calendar, but fall about six hours later every year, amounting to one full day in four years. They are reset by the occurrence of a leap year. The Gregorian calendar is designed to keep the March equinox no later than 21 March as accurately as is practical. Also see: Gregorian calendar seasonal error.

The calendar equinox (used in the calculation of Easter) is 21 March, the same date as in the Easter tables current at the time of the Council of Nicaea in AD 325. The calendar is therefore framed to prevent the astronomical equinox wandering onto 22 March. From Nicaea to the date of the reform, the years 500, 600, 700, 900, 1000, 1100, 1300, 1400 and 1500, which would not have been leap years in the Gregorian calendar, amount to nine days, but astronomers directed that ten days be removed.

Currently, the most common equinox and solstice dates are March 20, June 21, September 22 or 23 and December 21; the four-year average slowly shifts to earlier times as the century progresses. This shift is a full day in about 128 years (compensated mainly by the century "leap year" rules of the Gregorian calendar) and as 2000 was a leap year the current shift has been progressing since the beginning of the last century, when equinoxes and solstices were relatively late. This also means that in many years of the twentieth century, the dates of March 21, June 22, September 23 and December 22 were much more common, so older books teach (and older people may still remember) these dates.

Note that all the times are given in UTC (w:Coordinated Universal Time—roughly speaking, the time at w:Greenwich, ignoring w:British Summer Time). People living farther to the east (Asia and Australia), whose local times are in advance, will see the astronomical seasons apparently start later; for example, in w:Tonga (UTC+13), an equinox occurred on September 24, 1999, a date which will not crop up again until 2103. On the other hand, people living far to the west (America) whose clocks run behind UTC may experience an equinox as early as March 19.

Change over time

Over thousands of years, the Earth's w:axial tilt and orbital eccentricity vary (see w:Milankovitch cycles). The equinoxes and solstices move westward relative to the stars while the perihelion and aphelion move eastward. Thus, ten thousand years from now Earth's northern winter will occur at aphelion and northern summer at perihelion. The severity of seasonal change — the average temperature difference between summer and winter in location — will also change over time because the Earth's axial tilt fluctuates between 22.1 and 24.5 degrees.

Smaller irregularities in the times are caused by perturbations of the Moon and the other planets.

my own calculations

dekadays in 2782 YEA by w:Gregorian Calendar
1st Dekaday 21 December 2019 to 30 December 2020
2nd Dekaday 31 December 2019 to 9 January 2020
3rd Dekaday 10 January 2020 to 19 January 2020
4th Dekaday 20 January 2020 to 29 January 2020
5th Dekaday 30 January 2020 to 8 February 2020
6th Dekaday 9 February 2020 to 18 February 2020
7th Dekaday 19 February 2020 to 28 February 2020
8th Dekaday 29 February 2020 to 9 March 2020
9th Dekaday 10 March 2020 2020 to 19 March 2020
10th Dekaday 19 March 2020 2020 to 28 March 2020
11th Dekaday 29 March 2020 2020 to 7 April 2020
12th Dekaday 8 April 2020 to 17 April 2020
13th Dekaday 18 April 2020 to 28 April 2020
14th Dekaday 29 April 2020 to 8 May 2020
15th Dekaday 9 May 2020 to 18 May 2020
16th Dekaday 19 May 2020 to 28 May 2020
17th Dekaday 29 May 2020 to 7 June 2020
18th Dekaday 8 June 2020 to 17 June 2020
19th Dekaday 18 June 2020 to 27 June 2020
20th Dekaday 28 June 2020 to 7 July 2020
21st Dekaday 8 July 2020 to 17 July 2020
22nd Dekaday 18 July 2020 to 27 July 2020
23rd Dekaday 28 July 2020 to 6 August 2020
24th Dekaday 7 August 2020 to 16 August 2020
25th Dekaday 17 August 2020 to 26 August 2020
26th Dekaday 27 August 2020 to 5 September 2020
27th Dekaday 6 September 2020 to 15 September 2020
28th Dekaday 16 September 2020 to 25 September 2020
29th Dekaday 26 September 2020 to 5 October 2020
30th Dekaday 6 October 2020 to 15 October 2020
31st Dekaday 16 October 2020 to 25 October 2020
32nd Dekaday 26 October 2020 to 4 November 2020
33rd Dekaday 5 November 2020 to 14 November 2020
34th Dekaday 15 November 2020 to 24 November 2020
35th Dekaday 25 November 2020 to 4 December 2020
36th Dekaday 5 December 2020 2020 to 14 December 2020
(last 6 days of year) 15 December 2020 to 20 December 2020
dekadays in 2783 YEA by w:Gregorian Calendar
1st Dekaday 21 December 2020 to 30 December 2020
2nd Dekaday 31 December 2020 to 9 January 2021
3rd Dekaday 10 January 2021 to 19 January 2021
4th Dekaday 20 January 2021 to 29 January 2021
5th Dekaday 30 January 2021 to 8 February
6th Dekaday 9 February 2021 to 18 February 2021
7th Dekaday 19 February 2021 to 28 February 2021
8th Dekaday 1 March 2021 to 10 March 2021
9th Dekaday 11 March 2021 to 20 March 2021
10th Dekaday 21 March 2021 to 30 March 2021
11th Dekaday 31 March 2021 to 9 April 2021
12th Dekaday 10 April 2021 to 19 April 2021
13th Dekaday 20 April 2021 to 29 April 2021
14th Dekaday 30 April 2021 to 9 May 2021
15th Dekaday 10 May 2021 to 19 May 2021
16th Dekaday 20 May 2021 to 29 May 2021
17th Dekaday 30 May 2021 to 8 June 2021
18th Dekaday 9 June 2021 to 18 June 2021
19th Dekaday 19 June 2021 to 28 June 2021
20th Dekaday 29 June 2021 to 8 July 2021
21st Dekaday 9 July 2021 to 18 July 2021
22nd Dekaday 19 July 2021 to 28 July 2021
23rd Dekaday 29 July 2021 to 7 August 2021
24th Dekaday 8 August 2021 to 17 August 2021
25th Dekaday 18 August 2021 to 27 August 2021
26th Dekaday 28 August 2021 to 6 September 2021
27th Dekaday 7 September 2021 to 16 September 2021
28th Dekaday 17 September 2021 to 26 September 2021
29th Dekaday 27 September 2021 to 6 October 2021
30th Dekaday 7 October 2021 to 16 October 2021
31st Dekaday 17 October 2021 to 26 October 2021
32nd Dekaday 27 October 2021 to 5 November 2021
33rd Dekaday 6 November 2021 to 15 November 2021
34th Dekaday 16 November 2021 to 25 November 2021
35th Dekaday 26 November 2021 to 5 December 2021
36th Dekaday 6 December 2021 to 15 December 2021
last 5 days of year Dekaday 16 December 2021 to 20 December 2021
dekadays in 2784 YEA by w:Gregorian Calendar
1st Dekaday 21 December 2021 to 30 December 2021
2nd Dekaday 31 December 2021 to 9 January 2022
3rd Dekaday 10 January 2022 to 19 January 2022
4th Dekaday 20 January 2022 to 29 January 2022
5th Dekaday 30 January 2022 to 8 February 2022


see also