Title text: The month names are the same, except that the fourth month only has the name 'April' in even-numbered years, and is otherwise unnamed.
This comic pokes fun of attempts to "fix" the calendar by making it simpler or more rational, which inevitably result in a system just as complicated. This is an example of the paradox in complexity theory that if you attempt to simplify a system of problems by creating a new system of evaluation for the problems you often have instead made the problem more complex than it was originally.
Randall advertises his idea for a "Universal Calendar for a Universal Planet". He combines calendar definitions with time zone definitions. The abbreviation EST in this comic stands for Earth Standard Time (hence the title), but it is in itself a joke on the American Eastern Standard Time. In the rest of the explanation EST refers to the comic's Earth Standard Time!
 Length of year
Because there are approximately 365.2422 days in a solar year, various calendars use different means to keep the calendar year in sync with the solar year and the seasons. The Julian Calendar, for example, has leap days every four years, giving it an average year length of 365.25 days. The most widely used system is the Gregorian Calendar, which also has leap days every four years, but skips leap days in years divisible by 100 unless the year is also divisible by 400, the latter additions come from Earth's axial precession. This gives it an average year length of 365.2425 days, which is very close to the length of a solar year (see detailed explanation in this video: Earth's motion around the Sun, not as simple as I thought.
Other calendars have been proposed, such not counting leap days and special "festival days" as a day of the week, in order to make every date fall on the same day of the week every year.
- At "24 hours 4 minutes", EST days are longer, though there are only 360 of them in the year. The extra 4 minutes over the course of 360 days adds up to one standard day, so Randall's EST calendar would at this point have a year that is 361 standard days long. The 24 hours plus 4 minutes length may be a reference to sidereal day, whose duration is 24 hours minus 4 minutes.
- Running the clock backwards for 4 hours after every full moon gives 8 additional hours at each full moon, twelve or thirteen times in a year. Because a thirteenth full moon will occur once every 2.7 solar years on average, this modification adds 4.1228 standard days to an EST year, bringing it to 365.1228 days.
- The doubling of the non-prime numbers of the first non-reversed hour after each solstice and equinox is a final, very complicated way to bring Randall's EST year in extremely close sync with the solar year. There are 17 prime numbers between 0 and 59 and 43 non-primes. There are 2 equinoxes and 2 solstices each year, so a total of 4x43 = 172 minutes will occur twice. This brings the average length of Randall's EST year to 365.2422 standard days, equal to the solar year to four decimal places.
 Claimed benefits
Many of the claimed benefits for the calendar are highly dubious:
- While it is fairly simple to describe, EST is far from simple to understand or put in practice. Clocks in particular would have to regularly undertake very complicated processes like running backwards or duplicating non-prime minutes.
- EST does appear to be fairly clearly defined.
- EST fails completely to be unambiguous. Following each full moon, four hours occur three times, twice forward and once backward. Several minutes are also duplicated, making times during those periods ambiguous.
- The only way EST is free of historical baggage is that it breaks free of any sensible bits of historical baggage; it keeps such things as the 30-day month and 12-month year, but adopts a different (and variable) length of day that would make it wildly out of sync with the Earth's day-night cycle.
- EST is compatible with old units, as far as seconds, minutes, and hours are concerned, though not for days, months, or years.
- EST is indeed very precisely synced with the solar cycle. The joke is that this has nothing to do with the day/night cycle or the Earth's yearly orbital cycle; the solar cycle is a period of magnetic fluctuation within the sun, lasting 11 Earth years.
- EST is free of leap years, though some EST years are 8 hours longer than others on account of having an extra full moon.
- A calendar amenable to date math makes it easy to find the length of time between two dates and times by having standardized periods of time. The complex variability of the length of EST years, days, and hours mean it is only intermittently amenable to date math, which is to say not at all.
 Other features
The features of the calendar get increasingly bizarre as the description proceeds:
- The Epoch for EST is set by reference to the Julian calendar, which was superseded by the Gregorian calendar. The Julian calendar is currently 13 days behind the Gregorian calendar.
- The different zone for the United Kingdom is a reference to 1 yard being equal to 0.9144 meters, a pun on using imperial units instead of the metric system. This has been the joke before in 526: Converting to Metric and is also mentioned in 1643: Degrees.
- Randall does not like Daylight saving time (DST) very much, as has been made clear in several comics both before and after this one. See Narnian time below.
- Narnian time is a reference to the fictitious world of Narnia in CS Lewis' book The Lion, The Witch and The Wardrobe and its sequels. In Narnia, time passes much more quickly than in the real world. You could be in Narnia for several days and only a few minutes would have passed in the real world. However, synchronizing this effect would be impossible because it is not a consistent rate; it fluctuates wildly based on the whims of drama and magic. This and the DST mentioned above should be seen as a pair. Because when a country goes into DST time may not pass, which is basically what happens (more or less) when a child enters into Narnia. Whereas in EST Narnian time is synchronized to normal time, which DST is but for the one hour difference in the real calender. Using the wired Narnian time was used as the plot in the bottom left drawing in 821: Five-Minute Comics: Part 3.
- The Gregorian calendar does not include the year "0"; after "1" BC the next year is "1" AD. Randall's invention fixes this according to correct Mathematics, only to reintroduce the problem immediately by arbitrarily omitting the year 1958. The year 1958 is significant because January 1, 1958 is the epoch (time zero) in International Atomic Time (TAI), which is part of the basis for Coordinated Universal Time (UTC). (The main difference is that TAI doesn't add leap seconds.)
- The title text's concept of only naming the fourth month April in the even numbered years, and then leave it unnamed the other years, may be a reference to the ancient (Pre-Babylonian Exile) Jewish Calendar, which did not name the months, rather assigning them numbers from 1 to 12 (or 13 in leap years, where an extra month was added instead of an extra day). The names used by Jews today are the names of the Babylonian months, derived from various Babylonian deities or events in Jewish history or on the calendar.
- [Caption and text above the main panel:]
- xkcd presents
- Earth Standard Time
- A universal calendar for a universal planet
- EST is...
- Simple • Clearly defined • Unambiguous
- Free of historical baggage • Compatible with old units
- Precisely synced with the solar cycle • Free of leap years
- Intermittently amenable to date math
- [A list of the details concerning EST:]
Second: 1 S.I. second Minute: 60 seconds Hour: 60 minutes Day: 1444 minutes
(24 hours 4 minutes)
Month: 30 Days Year: 12 months
- For 4 hours after every full moon, run clocks backward.
- The non-prime-numbered minutes of the first full non-reversed hour after a solstice or equinox happen twice.
Epoch Time Zones 00:00:00 EST The two EST time zones are January 1, 1970
= 00:00:00 GMT
EST and EST (United Kingdom) January 1, 1970
These are the same except that the
UK second is 0.9144 standard seconds
Daylight saving: Countries may enter DST, but no time may pass there. Narnian Time: Synchronized✔ Year Zero: EST does have a year 0. (However, there is no 1958.)
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