Web reference sites:
http://www.wincalendar.com/
http://www.web-holidays.com/
http://www.timeanddate.com/
http://www.when-is.com/
http://www.bank-holidays.com/
http://www.mypanchang.com/ (Hindu calendar, "panchang" being calendar,
w/plural "panchangam")
http://www.interfaithcalendar.org/
Holidays with fixed, simple Gregorian dates:
New Year's Day / Nyttårsdag Jan 1
Kwanzaa ends Jan 2
Epiphany Jan 6
Inauguration Day (years divisible by 4, plus 1) Jan 20
Groundhog Day / Imbolc / Candlemas Feb 2
Emperor Norton's Birthday Feb 4
Samefolkets dag / Saami People's Day (Norway) Feb 6
Lincoln's Birthday Feb 12
Valentine's Day Feb 14
Flag Day, Canada Feb 15
Washington's Birthday Feb 22
International Women's Day Mar 8
St. Patrick's Day Mar 17
Spring Equinox / Ostara / Eostar / Eostre Mar 20
Cesar Chavez Day (California) Mar 31
April Fools Day Apr 1
Yuri's Night Apr 12
Earth Day Apr 22
May Day / Beltane May 1
Cinco de Mayo (Battle of Puebla) May 5
Frigjøringsdag (Liberation Day) May 8
Syttende Mai / Grunnlovsdagen / Nasjonaldagen, Norway May 17
Victoria Day, Canada May 18
Unionsoppløsningen (Union Dissolution Day), Norway Jun 7
Flag Day Jun 14
Bloomsday Jun 16
Juneteenth Jun 19
Summer Solstice / Midsummer Day / Midsommardagen Jun 20
Canada Day (was: Dominion Day) Jul 1
Independence Day Jul 4
Bastille Day Jul 14
Lammas / Lughnasadh Aug 1
Admission Day (California) Sep 9
Autumnal Equinox / Mabon / Harvest Home Sep 22
Mohandas K. Gandhi's birthday (1869) Oct 2
Leif Ericson (Leiv Eiriksson) Day Oct 9
Columbus Day (original date per 1934-1971 law) Oct 12
Ovshinsky Day http://www.newstatesman.com/2013/10/remember-japans-yankee-genius Oct 17
United Nations Day Oct 24
All Hallows Eve / Halloween / Samhain Oct 31
All Saints' Day / Dia de los Muertos Nov 1
All Souls' Day / Dia de los Muertos Nov 2
Guy Fawkes Day Nov 5
Veterans' Day (was: Armistice Day) (Rememberance Day in Canada) Nov 11
Sadie Hawkins Day Nov 13
Luciadagen (St. Lucia's Day), Scandinavia Dec 13
Winter Solstice / Yule Dec 21
Christmas Eve / Julaften Dec 24
Christmas Day / Jul Dec 25
Boxing Day / St. Stephen's Day Dec 26
Kwanzaa begins Dec 26
New Year's Eve / Nyttår Dec 31
Holidays with formulas based on the Gregorian calendar:
2020 2021 2022 2023
Martin Luther King Day (3rd Mon Jan) Jan20 Jan18 Jan17 Jan16
Presidents' Day (3rd Mon Feb) Feb17 Feb15 Feb21 Feb20
Superb Owl Sunday (1st Sun Feb) Feb2 Feb7 Feb6 Feb 5
https://www.reddit.com/r/Superbowl/
DST begins (2nd Sun Mar) Mar8 Mar14 Mar13 Mar12
Mothers' Day / Morsdag (2nd Sun May) May10 May9 May8 May14
Armed Forces Day (3rd Sat May) May16 May15 May21 May20
Memorial Day (last Mon May) May30 May31 May30 May29
Fathers' Day / Farsdag (3rd Sun Jun) Jun21 Jun20 Jun19 Jun18
Labour Day (1st Mon Sep) Sep7 Sep6 Sep5 Sep4
Columbus Day observed (2nd Mon Oct) Oct12 Oct11 Oct10 Oct9
Thanksgiving Day in Canada (2nd Mon Oct) Oct12 Oct11 Oct10 Oct9
DST ends (1st Sun Nov) Nov1 Nov7 Nov6 Nov5
Thanksgiving Day, USA (4th Thu Nov) Nov26 Nov26 Nov25 Nov24
Advent (4th Sunday before Christmas) Nov29 Nov28 Nov27 Dec3
Fed Election Day (1st Tue after 1st Mon Nov3 - Nov8 -
in Nov, in even-numbered years)
Holidays defined as Christian moveable holidays:
2020 2021 2022 2023
Ash Wednesday (46 days before Easter) Feb26 Feb17 Mar2 Feb22
Palm Sunday (7 days before Easter) Apr05 Mar28 Apr10 Apr2
Good Friday (2 days before Easter) Apr10 Apr2 Apr15 Apr7
Easter (first Sunday on or following the Apr12 Apr4 Apr17 Apr9
spring Equinox after the full moon
Easter Monday, Canada and UK Apr13 Apr5 Apr18 Apr10
Orthodox Easter (EasterDay of EasterMonth Apr19 May2 Apr24 Apr16
in the Julian Calendar -- don't ask!
Ascension Day (40 days after Easter) May21 May13 May26 May18
Pentecost / Whitsunday (7th Sun after May31 May23 Jun5 May28
Easter)
Holidays defined per the Jewish calendar:
2020 2021 2022 2023
Tu B'Shevat (15 Shevat) Feb10 Jan28 Jan17 Feb6
Purim (14/15 Adar) Mar10 Feb27 Mar18 Mar8
Pesach (Passover) starts (15 Nisan) Apr09 Mar28 Apr16 Apr6
Pesach ends, Reform practice (21 Nisan) Apr15 Apr3 Apr22 Apr12
Pesach ends (22 Nisan in diaspora) Apr16 Apr4 Apr23 Apr13
Yom Ha Atzma'ut (5 Iyar) Apr27 Apr14 May4 Apr25
Shavuot (6/7 Sivan) May28 May17 Jun5 May26
Tisha B'Av (9 Av) Jul29 Jul18 Aug7 Jul27
Rosh Ha Shana (1 Tishrei) Sep18 Sep7 Sep26 Sep16
(5781)(5782)(5783)(5784)
Yom Kippur (10 Tishrei) Sep28 Sep16 Oct5 Sep25
Sukkot starts (15 Tishrei) Oct3 Sep21 Oct10 Sep30
Sukkot ends, (22 Tishrei in diaspora) Oct9 Sep27 Oct16 Oct6
Shemini Atzeret begins (22 Tishrei) Oct9 Sep27 Oct16 Oct6
Simchat Torah (23 Tishrei in diaspora) Oct10 Sep28 Oct17 Oct7
Hanukkah starts (25 Kislev) Dec10 Nov28 Dec18 Dec8
Hanukkah ends (3 or 4 Tevet) Dec18 Dec6 Dec26 Dec16
Holidays defined per the Hijra (Muslim) calendar:
2020
Mawlid an Nabi (10 Rabi al-Awwal) Oct29 Oct18 Oct8 Sep27
Lailat al Miraj (27 Rejab) Mar22 Mar11 Feb28 Feb18
Lailat al Bara'ah (15 Sha'ban) Apr08 Mar28 Mar18
Ramadan starts (1 Ramadan) Apr24 Apr13 Apr2 Mar23
Eid al Fitr (1 Shawwal) May24 May13 May2 Apr21
(May your feast be blessed)
Waqf al Arafa (9 Dhu al-Hijja) Jul29 Jul30 Jul19 Jul8
Eid al Adha (10 Dhu al-Hijja) Jul31 Jul31 Jul9 Jun28
Hijra New Year (1 Muharram) Aug20 Aug9 Jul30 Jul19
(1442)
Ashura (10 Muharram) Aug29 Aug18 Aug8 Jul28
Hijra month order:
Muharram (30 days), Safar (29 days), Rabi al-Awwal (30 days),
Rabi al-Thany (29 days), Jumaada al-Awwal (30 days),
Jumaada al-Thany (29 days), Rajab (30 days), Sha'ban (29 days),
Ramadan (30 days), Shawwal (29 days), Dhu al-Qa'da (30 days),
Dhu al-Hijja (29/30 days).
Holidays in the Chinese Calendar
2020 2021 2022 2023
Kitchen God Festival / Little New Year Jan18
Chinese New Year / Spring Festival Jan25 Feb12 Feb1 Jan22
Rat Ox Tiger Rabbit
or goat
Lantern Festival Feb08 Feb26 Feb15 Feb5
Qingming Festival Apr04 Apr5 Apr5 Apr5
Dragon Boat Festival Jun25 Jun14 Jun3 Jun22
Night of Sevens Aug25
Ghost Festival / Spirit Festival Sep02 Aug22 Aug12 Aug30
Mid-Autumn Festival / Moon Festival Oct01 Sep21 Sep10 Sep29
Double Ninth Festival / Double Yang Oct25 Oct14 Oct4 Oct23
Xia Yuan Festival / Spirit Festival Nov29
Winter Solstice Festival Dec21
Holidays in the Hindu Calendar (day is technically sunrise to sunrise)
2020 2021 2022 2023
Holi / Phagwah / Doul Jatra /
Basanta-Utsab (3 - 16 days, depending)
First day is called Holi Dhulandi Mar09 Mar28 Mar18 Mar7
Rama Navami (9th day of Chaitra) Apr02 Apr21 Apr10 Mar30
Krishna Janmashtami / Janmasthami Aug11 Aug29 Aug18 Sep6
http://www.when-is.com/krishna-janmaashtami.asp
Ganesh Chaturthi (10 days) Aug22 Sep10 Aug31 Sep19
Navratri / Navaratri (nine nights and
ten days) Oct17 Oct6
Durga Puja / Durgotsava (5 days) Oct22
Vijaya Dashami (last day of Navaratri) Oct25
Chhath / Dala Chhath (6th day of Kartik) Nov20
Diwali (begins, 5 days) Nov14 Nov4 Oct24 Nov9
By the way, 32-bit Unix date rollover will be
Tue Jan 19 03:14:08 2038 -- 2**31 = 2,147,483,648 seconds after the
epoch of Thu Jan 01 00:00:00 1970 when Unix time began.