Time

In search of the perfect date...

Nice post about time:

• https://ourworldindata.org/time-use

Calculate the day of the week

Calculate a number for each of the day, month, and year by adding the digits together as follows:

In this example todays date is 15. June 2023:

Day = just todays day e.g. 15 of June

Month = the number of below table e.g. for June = 3

Years = the number of below table e.g. for 2023 = 0

When calculating the year, either memorize the table or calculate the value using the last two digits e.g. for 2023 = 23. Take 23, divide it by 4, and round down, then add it back to itself. Eg. 23/4 = 5 (rounded down). Adding this to itself we get 28 (23+5). Now, we get the remainder after dividing by 7. In our case of 28, the remainder after division by 7 is 0.

If the year is in the 20th century (1900-1999), add +1. The algorithm will not work for dates before 1582. In our example we add 0. For other centuries use this overview:

If the date is January or February of a leap year, then subtract 1 to the final answer. Here is a list of leap years from 1804-2400:

So finally, in our example we add 15+3+0+0+0 = 18 and get the remainder when dividing the result by 7 = 4.

According to the table below 4 = Thursday so 15. June 2023 was a Thursday :)

The full formula looks like this:

Remainder of (Day + Month(Table) + Year(Table) + Century + (if leap year + 1))/7 = value to look up in day of the week table.

Time zone

Some links to time zone standards:

• ISO 8601 Wikipedia https://en.wikipedia.org/wiki/ISO_8601
• ISO 8601 https://www.iso.org/obp/ui/#iso:std:iso:8601:-1:ed-1:v1:en
• ISO Weekdate Wikipedia https://en.wikipedia.org/wiki/ISO_week_date
• RFC 3339 https://tools.ietf.org/html/rfc3339
• Extended Date/Time Format (EDTF): https://www.loc.gov/standards/datetime/

A list of time zones:

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

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

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.

Metric Time

Sources:

• https://en.wikipedia.org/wiki/Metric_time
• https://timeity.com/metric-time/

Calendar

List of calendars: https://en.wikipedia.org/wiki/List_of_calendars

Representation in various calendars of the year 2021

Non 7-day weeks

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

• Discworld
• Middle-earth
• Star Trek (Stardates)

Links

• 120 years of timezones: https://blog.scottlogic.com/2021/09/14/120-years-timezone.html
• https://en.wikipedia.org/wiki/ISO_3166-1
• https://www.timeanddate.com/time/zones/
• https://www.iana.org/time-zones
• https://www.ibm.com/docs/en/workload-scheduler/8.6.0?topic=zones-complete-table-time-variable-length-notation

Wikipedia on time, calendars and dates

• https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
• https://en.wikipedia.org/wiki/List_of_dates_predicted_for_apocalyptic_events
• https://en.wikipedia.org/wiki/List_of_unusual_units_of_measurement#Time
• https://en.wikipedia.org/wiki/Soviet_calendar
• https://en.wikipedia.org/wiki/Hanke%E2%80%93Henry_Permanent_Calendar