Calendars ,days of the week , and dates

There are different calendar systems that are still used or were used in the past . Examples include the Julian calendar , the Gregorian calendar , the Hebrew calendar , the Islamic and the Iranian calendars , the French Republican calendar , etc. Most calendars use astronomical events and cycles as their basis: the day is based on the rotation of planet Earth on its axis , the month is based on the Moon revolving around the Earth , and the year is based on the period of revolution of the Earth around the Sun.The influence of the gravitational force from other planets may cause the length of a particular year to vary by several minutes. The Gregorian calendar was introduced in 1582 .Dates before October 1582 are usually given in the Julian calendar .

Here is a list of leap years in the Gregorian calendar from 2016 to 2416 (done with the help of Mathematica) :

2016 , 2020 , 2024 , 2028 , 2032 , 2036 , 2040 , 2044 , 2048 , 2052 , 2056 , 2060 , 2064 , 2068 , 2072 , 2076 , 2080 , 2084 , 2088 , 2092 , 2096 , 2104 , 2108 , 2112 , 2116 , 2120 , 2124 , 2128 , 2132 , 2136 , 2140 , 2144 , 2148 , 2152 , 2156 , 2160 , 2164 , 2168 , 2172 , 2176 , 2180 , 2184 , 2188 , 2192 , 2196 , 2204 , 2208 , 2212 , 2216 , 2220 , 2224 , 2228 , 2232 , 2236 , 2240 , 2244 , 2248 , 2252 , 2256 , 2260 , 2264 , 2268 , 2272 , 2276 , 2280 , 2284 , 2288 , 2292 , 2296 , 2304 , 2308 , 2312 , 2316 , 2320 , 2324 , 2328 , 2332 , 2336 , 2340 , 2344 , 2348 , 2352 , 2356 , 2360 , 2364 , 2368 , 2372 , 2376 , 2380 , 2384 , 2388 , 2392 , 2396 , 2400 , 2404 , 2408 , 2412 , 2416 .

In the Gregorian calendar , most years that are multiples of 4 are leap years . The years 2100, 2200, 2300 are not leap years .

Below is a list of the days of the week each one corresponding to the first day of the year (Gregorian calendar) from the year  2016 to 2036 :

  • 1/1/2016 : Friday.
  • 1/1/2017 : Sunday.
  • 1/1/2018 :Monday.
  • 1/1/2019: Tuesday.
  • 1/1/2020: Wednesday.
  • 1/1/2021: Friday.
  • 1/1/2022: Saturday.
  • 1/1/2023: Sunday.
  • 1/1/2024: Monday.
  • 1/1/2025: Wednesday.
  • 1/1/2026: Thursday.
  • 1/1/2027: Friday.
  • 1/1/2028: Saturday.
  • 1/1/2029: Monday.
  • 1/1/2030: Tuesday.
  • 1/1/2031: Wednesday.
  • 1/1/2032: Thursday.
  • 1/1/2033: Saturday.
  • 1/1/2034: Sunday.
  • 1/1/2035: Monday.
  • 1/1/2036: Tuesday.

Next I give the day of the week corresponding to the 4th of July from the year 2015 to 2020:

  • 2015: 4th of July is a Saturday.
  • 2016: 4th of July is a Monday.
  • 2017: Tuesday.
  • 2018: Wednesday.
  • 2019: Thursday.
  • 2020: Saturday.

The day of the week corresponding to the 14th of July (Bastille day in France) from the year 2015 to 2020:

  • 2015: 14th of July is a Tuesday.
  • 2016: Thursday.
  • 2017: Friday.
  • 2018: Saturday.
  • 2019: Sunday.
  • 2020: Tuesday.

Easter Sunday date (Western churches and Greek Orthodox churches) for 4 years:

  • 27 March 2016 (Western), 1 May 2016 (Greek Orthodox).
  • 16 April 2017 , same date for Greek Orthodox churches.
  • 1 April 2018 , 8 April 2018.
  • 21 April 2019 , 28 April 2019.

Here are days of the week corresponding to some important historical dates and people (after 1582 the dates are in the Gregorian calendar) :

  • The most accepted date for the Death of Genghis Khan  ( Julian calendar) is 18 August 1227 , which was a Wednesday.The date in the Gregorian calendar would be  Wednesday 25 August 1227.
  • Columbus reached America : Friday 10 October 1492 (Julian calendar). The date in the Gregorian calendar would be Friday 21 October 1492.
  • First publication of Philosophiæ Naturalis Principia Mathematica by Isaac Newton: Saturday 5 July 1687 ( Gregorian).
  • Date of birth of Carl Friedrich Gauss : Wednesday 30 April 1777.
  • Date of death of Carl Friedrich Gauss: Friday 23 February 1855.
  • Death of Napoleon Bonaparte : Saturday 5 May 1821.
  • Date of birth of Jules Verne : Friday 8 February 1828.
  • Date of birth of Pierre Simon Laplace : Wednesday 23 April 1749.
  • Death of Pierre Simon Laplace : Thursday 5 April 1827.

Another day of the week and date: Sunday , 31 July 2072 (this date is somewhat important for me).

The Islamic calendar is a lunar calendar ( based on the motion and phases of the Moon) of 12 months  with alternating months of 29 and 30 days , and  a year made of 354 days , which is about 11 days shorter than the length of the year in the Gregorian calendar. In the table below I give the day of the week corresponding to the first day of the year (Islamic calendar) and the corresponding Gregorian date for a number of consecutive years:

Year(Islamic calendar) First day of the year Gregorian date
1/1/1437  Thursday  15 October 2015
1/1/1438  Monday  3 October 2016
 1439  Friday  22 September 2017
 1440  Wednesday  12 September 2018
 1441  Sunday  1 September 2019
 1442  Thursday  20 August 2020
 1443  Tuesday  10 August 2021
 1444  Saturday  30 July 2022
 1445  Wednesday  19 July 2023
 1446  Monday  8 July 2024
 1447  Friday  27 June 2025
 1448  Wednesday  17 June 2026
 1449  Sunday  6 June 2027
 1450  Thursday  25 May 2028
 1451  Tuesday  15 May 2029
 1452  Saturday  4 May 2030
 1453  Wednesday  23 April 2031
 1454  Monday  12 April 2032
 1455  Friday  1 April 2033
 1456  Tuesday  21 March 2034
1457 Sunday 11 March 2035
1458 Thursday 28 February 2036
1459 Tuesday 17 February 2037
1460 Saturday 6 February 2038
1461 Wednesday 26 January 2039
1462 Monday 16 January 2040
1463 Friday 4 January 2041
1464 Tuesday 24 December 2041
1465 Sunday 14 December 2042
1466 Thursday 3 December 2043
1467 Tuesday 22 November 2044

A good online calendar converter can be found in here.

A number of scholars , thinkers and scientists in the past  have written books and studies about calendars , the chronology of world history and historical events (such as Isaac Newton’s The Chronology of Ancient Kingdoms and al Biruni‘s The Chronology of Ancient Nations , also known as The Remaining Signs of Past Centuries).

Newton Chronology of ancient kingdoms

However , historical chronology and dates before the beginning of the Christian Era are mostly approximate , uncertain or imprecise. Therefore I think a better and more accurate chronology of ancient History (and of World History in general) ought to be constructed , using rigorous historiographical and historical methods , and unbiased scientific reasoning , analysis , and methods.

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