User:DMBFFF/Dekadays beginning from winter solstice
links to and content forked from Wikipedia
w:December solstice
w:Winter solstice
w:Season#Astronomical
Astronomical
| 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.
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 |
| dekadays in 2785 YEA | by w:Gregorian Calendar | by w:International Fixed Calendar, International Fixed Calendar |
|---|---|---|
| 17th Dekaday | 31 May 2023 to 9 June 2023 | 11 June 2023 to 20 June 2023 |
| 18th Dekaday | 10 June 2023 to 19 June 2023 | 21 June 2023 to 2 Sol 2023 |
| 19th Dekaday | 20 June 2023 to 29 June 2023 | 3 Sol 2023 to 12 Sol 2023 |
| 20th Dekaday | 30 June 2023 to 9 July 2023 | 13 Sol 2023 to 22 Sol 2023 |
| 21st Dekaday | 10 July 2023 to 19 July 2023 | 23 Sol 2023 to 4 July 2023 |
| 22nd Dekaday | 20 July 2023 to 29 July 2023 | 5 July 2023 to 14 July 2023 |
| 23rd Dekaday | 30 July 2023 to 8 August 2023 | 15 July 2023 to 24 July 2023 |
| 24th Dekaday | 9 August 2023 to 18 August 2023 | 25 July 2023 to 6 August 2023 |
| 25th Dekaday | 19 August 2023 to 28 August 2023 | 7 August 2023 to 16 August 2023 |
| 26th Dekaday | 29 August 2023 to 7 September 2023 | 17 August 2023 to 26 August 2023 |
| 27th Dekaday | 8 September 2023 to 17 September 2023 | 27 August 2023 to 8 September 2023 |
| 28th Dekaday | 18 September 2023 to 27 September 2023 | 9 September 2023 to 18 September 2023 |
| 29th Dekaday | 28 September 2023 to 7 October 2023 | 19 September 2023 to 28 September 2023 |
| 30th Dekaday | 8 October 2023 to 17 October 2023 | 1 October 2023 to 10 September 2023 |
| 32nd Dekaday | 28 October 2023 to 6 November 2023 | 21 October 2023 to 2 November 2023 |
| 33rd Dekaday | 7 November 2023 to 16 November 2023 | 3 November 2023 to 12 November 2023 |
| 34th Dekaday | 17 November 2023 to 26 November 2023 | 13 November 2023 to 22 November 2023 |
| 35th Dekaday | 27 November 2023 to 6 December 2023 | 23 November 2023 to 4 December 2023 |
see also
- Fun:Song(s) for the dekaday
- w:Cross-quarter day which re-directs to w:Wheel of the Year
- Cross-quarter day (earlier version)
- w:Solar term