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xkcd_iso_8601 perfect-date

Time zone

Some links to time zone standards:

A list of time zones:

10 Azores Standard Time (GMT-01:00) Azores Atlantic/Azores
12 Cape Verde Standard Time (GMT-01:00) Cape Verde Islands Atlantic/Cape_Verde
43 Mid-Atlantic Standard Time (GMT-02:00) Mid-Atlantic Atlantic/South_Georgia
27 E. South America Standard Time (GMT-03:00) Brasilia America/Sao_Paulo
58 SA Eastern Standard Time (GMT-03:00) Buenos Aires, Georgetown America/Argentina/Buenos_Aires
35 Greenland Standard Time (GMT-03:00) Greenland America/Godthab
51 Newfoundland Standard Time (GMT-03:30) Newfoundland and Labrador America/St_Johns
06 Atlantic Standard Time (GMT-04:00) Atlantic Time (Canada) America/Halifax
60 SA Western Standard Time (GMT-04:00) Caracas, La Paz America/La_Paz
17 Central Brazilian Standard Time (GMT-04:00) Manaus America/Cuiaba
54 Pacific SA Standard Time (GMT-04:00) Santiago America/Santiago
59 SA Pacific Standard Time (GMT-05:00) Bogota, Lima, Quito America/Bogota
28 Eastern Standard Time (GMT-05:00) Eastern Time (US and Canada) America/New_York
70 US Eastern Standard Time (GMT-05:00) Indiana (East) America/Indiana/Indianapolis
15 Central America Standard Time (GMT-06:00) Central America America/Costa_Rica
21 Central Standard Time (GMT-06:00) Central Time (US and Canada) America/Chicago
22 Central Standard Time (Mexico) (GMT-06:00) Guadalajara, Mexico City, Monterrey America/Monterrey
11 Canada Central Standard Time (GMT-06:00) Saskatchewan America/Edmonton
71 US Mountain Standard Time (GMT-07:00) Arizona America/Phoenix
45 Mountain Standard Time (Mexico) (GMT-07:00) Chihuahua, La Paz, Mazatlan America/Chihuahua
44 Mountain Standard Time (GMT-07:00) Mountain Time (US and Canada) America/Denver
55 Pacific Standard Time (GMT-08:00) Pacific Time (US and Canada), Tijuana America/Tijuana
02 Alaskan Standard Time (GMT-09:00) Alaska America/Anchorage
38 Hawaiian Standard Time (GMT-10:00) Hawaii Pacific/Honolulu
61 Samoa Standard Time (GMT-11:00) Midway Island, Samoa Pacific/Apia
36 Greenwich Standard Time (GMT) Casablanca, Monrovia Africa/Monrovia
34 GMT Standard Time (GMT) Greenwich Mean Time : Dublin, Edinburgh, Lisbon, London Europe/London
75 W. Europe Standard Time (GMT+01:00) Amsterdam, Berlin, Bern, Rome, Stockholm, Vienna Europe/Berlin
18 Central Europe Standard Time (GMT+01:00) Belgrade, Bratislava, Budapest, Ljubljana, Prague Europe/Belgrade
56 Romance Standard Time (GMT+01:00) Brussels, Copenhagen, Madrid, Paris Europe/Paris
19 Central European Standard Time (GMT+01:00) Sarajevo, Skopje, Warsaw, Zagreb Europe/Belgrade
74 W. Central Africa Standard Time (GMT+01:00) West Central Africa Africa/Lagos
37 GTB Standard Time (GMT+02:00) Athens, Bucharest, Istanbul Europe/Istanbul
29 Egypt Standard Time (GMT+02:00) Cairo Africa/Cairo
64 South Africa Standard Time (GMT+02:00) Harare, Pretoria Africa/Harare
32 FLE Standard Time (GMT+02:00) Helsinki, Kiev, Riga, Sofia, Tallinn, Vilnius Europe/Riga
41 Israel Standard Time (GMT+02:00) Jerusalem Asia/Jerusalem
26 E. Europe Standard Time (GMT+02:00) Minsk Europe/Minsk
48 Namibia Standard Time (GMT+02:00) Windhoek Africa/Windhoek
05 Arabic Standard Time (GMT+03:00) Baghdad Asia/Baghdad
03 Arab Standard Time (GMT+03:00) Kuwait, Riyadh Asia/Kuwait
57 Russian Standard Time (GMT+03:00) Moscow, St. Petersburg, Volgograd Europe/Moscow
24 E. Africa Standard Time (GMT+03:00) Nairobi Africa/Nairobi
40 Iran Standard Time (GMT+03:30) Tehran Asia/Tehran
04 Arabian Standard Time (GMT+04:00) Abu Dhabi, Muscat Asia/Muscat
09 Azerbaijan Standard Time (GMT+04:00) Baku Asia/Baku
33 Georgian Standard Time (GMT+04:00) Tblisi Asia/Tbilisi
13 Caucasus Standard Time (GMT+04:00) Yerevan Asia/Yerevan
01 Afghanistan Standard Time (GMT+04:30) Kabul Asia/Kabul
30 Ekaterinburg Standard Time (GMT+05:00) Ekaterinburg Asia/Yekaterinburg
76 West Asia Standard Time (GMT+05:00) Islamabad, Karachi, Tashkent Asia/Tashkent
39 India Standard Time (GMT+05:30) Chennai, Kolkata, Mumbai, New Delhi Asia/Calcutta
49 Nepal Standard Time (GMT+05:45) Kathmandu Asia/Kathmandu
47 N. Central Asia Standard Time (GMT+06:00) Almaty, Novosibirsk Asia/Novosibirsk
16 Central Asia Standard Time (GMT+06:00) Astana, Dhaka Asia/Almaty
65 Sri Lanka Standard Time (GMT+06:00) Sri Jayawardenepura Asia/Colombo
46 Myanmar Standard Time (GMT+06:30) Yangon (Rangoon) Asia/Rangoon
62 SE Asia Standard Time (GMT+07:00) Bangkok, Hanoi, Jakarta Asia/Bangkok
53 North Asia Standard Time (GMT+07:00) Krasnoyarsk Asia/Krasnoyarsk
23 China Standard Time (GMT+08:00) Beijing, Chongqing, Hong Kong SAR, Urumqi Asia/Shanghai
52 North Asia East Standard Time (GMT+08:00) Irkutsk, Ulaanbaatar Asia/Irkutsk
63 Singapore Standard Time (GMT+08:00) Kuala Lumpur, Singapore Asia/Singapore
73 W. Australia Standard Time (GMT+08:00) Perth Australia/Perth
66 Taipei Standard Time (GMT+08:00) Taipei Asia/Taipei
68 Tokyo Standard Time (GMT+09:00) Osaka, Sapporo, Tokyo Asia/Tokyo
42 Korea Standard Time (GMT+09:00) Seoul Asia/Seoul
78 Yakutsk Standard Time (GMT+09:00) Yakutsk Asia/Yakutsk
14 Cen. Australia Standard Time (GMT+09:30) Adelaide Australia/Adelaide
07 AUS Central Standard Time (GMT+09:30) Darwin Australia/Darwin
25 E. Australia Standard Time (GMT+10:00) Brisbane Australia/Brisbane
08 AUS Eastern Standard Time (GMT+10:00) Canberra, Melbourne, Sydney Australia/Sydney
77 West Pacific Standard Time (GMT+10:00) Guam, Port Moresby Pacific/Guam
67 Tasmania Standard Time (GMT+10:00) Hobart Australia/Hobart
72 Vladivostok Standard Time (GMT+10:00) Vladivostok Asia/Vladivostok
20 Central Pacific Standard Time (GMT+11:00) Magadan, Solomon Islands, New Caledonia Pacific/Guadalcanal
50 New Zealand Standard Time (GMT+12:00) Auckland, Wellington Pacific/Auckland
31 Fiji Standard Time (GMT+12:00) Fiji Islands, Kamchatka, Marshall Islands Pacific/Fiji
69 Tonga Standard Time (GMT+13:00) Nuku'alofa Pacific/Tongatapu

Lunar Standard Time (LST)

The Lunar year consists of twelve days, named after the first men who walked on the Moon. Each day is divided into 30 cycles of time, with each cycle being divided into 24 moon-hours. Each moon-hour then has 60 moon-minutes, which in turn of course are made up of 60 moon-seconds each. The inverted triangle ∇ is the LST symbol, and if used it suffixes date and prefixes time. The standard notation is: Year-Day-Cycle ∇ Hour:Minute:Second example: 55-11-14 ∇ 14:36:49

Measure Terrestrial Time Lunar Time
seconds 1 0.9843529666671
minute 60 terrestrial seconds 60 lunar seconds
hour 60 terrestrial minutes 60 lunar minutes
day 24 terrestrial hours 30 lunar cycles*
year 365 days 12 lunar days

*Each is day named after one of the twelve men that walked on the Moon during the Apollo projects:

Day Name Days
Day 1 Armstrong 1-30
Day 2 Aldrin 1-30
Day 3 Conrad 1-30
Day 4 Bean 1-30
Day 5 Shepard 1-30
Day 6 Mitchell 1-30
Day 7 Scott 1-30
Day 8 Irwin 1-30
Day 9 Young 1-30
Day 10 Duke 1-30
Day 11 Cernan 1-30
Day 12 Schmitt 1-30

On the moon you have about 15 days of continuous daylight and then 15 days of total darkness. So, a "day" on the Moon, would correspond to about a month or 29.5 Earth-days. Once, about every 29 days, you have a full moon, which is "noon" on the center of the disk. This is also called the synodic month. So a day on the moon, counting from noon to noon, lasts about 29.27 to 29.83 Earth days. Neil Armstrong set foot on the Moon surface on July 21th 1969 at 02:56:15 UT, and this is the obvious choice for a point in time for the calendar to start. So, this is Year 1, day 1 cycle 1, 00:00:00.

You can use this tool to convert a time to lunar time:


Metric Time

Measure Time as we Know it Metric Time Usage
day 24 hours or 1,440 minutes or 86,400 seconds 10 hours or 1,000 minutes or 100,000 seconds
hour 60 minutes or 3,600 seconds 100 minutes or 10,000 seconds
minute 60 seconds 100 seconds



List of calendars:

Representation in various calendars of the year 2021

Calendar Year 2021
Gregorian calendar 2021 MMXXI
Ab urbe condita 2774
Armenian calendar 1470 ԹՎ ՌՆՀ
Assyrian calendar 6771
Bahá'í calendar 177–178
Balinese saka calendar 1942–1943
Bengali calendar 1428
Berber calendar 2971
British Regnal year 69 Eliz. 2 – 70 Eliz. 2
Buddhist calendar 2565
Burmese calendar 1383
Byzantine calendar 7529–7530
Chinese calendar 庚子年 (Metal Rat) 4717 or 4657 — to — 辛丑年 (Metal Ox) 4718 or 4658
Coptic calendar 1737–1738
Discordian calendar 3187
Ethiopian calendar 2013–2014
Hebrew calendar 5781–5782
Hindu calendar Vikram Samvat 2077–2078
Hindu calendar Shaka Samvat 1942–1943
Hindu calendar Kali Yuga 5121–5122
Holocene calendar 12021
Igbo calendar 1021–1022
Iranian calendar 1399–1400
Islamic calendar 1442–1443
Japanese calendar Reiwa 3 (令和3年)
Javanese calendar 1954–1955
Juche calendar 110
Julian calendar Gregorian minus 13 days
Korean calendar 4354
Minguo calendar ROC 110 民國110年
Nanakshahi calendar 553
Thai solar calendar 2564
Tibetan calendar 阳金鼠年 (male Iron-Rat) 2147 or 1766 or 994 — to — 阴金牛年 (female Iron-Ox) 2148 or 1767 or 995
Unix time 1609459200 – 1640995199

Non 7-day weeks

Tradition week length
Bali various
Korea 5 days
Java 5 days
Discordian 5 days
Akan 6 days
Ancient Rome 8 days
Burmese 8 days
Celtic 8 days
Baltic 9 days
Chinese 10 days
Egyptian Calendar 10 days
French Republican Calendar 10 days
Aztecs 13 days

Fun facts

A moment was a medieval unit of time. The movement of a shadow on a sundial covered 40 moments in a solar hour. An hour in this case meant one twelfth of the period between sunrise and sunset. The length of a solar hour depended on the length of the day, which in turn varied with the season, so the length of a moment in modern seconds was not fixed, but on average, a moment corresponded to 90 seconds.

Fictional calendars

Wikipedia on time, calendars and dates