Silican calendar

Convert a Gregorian date to a Silican date



The silican calendar is a calendar system in which each year has four seasons, each of which divided into thirteen weeks, each of which has seven days. Each week, season, and year starts on a Monday. The year uses the year in the Holocene calendar.


A few years ago, I discovered the New Earth Calendar, in which the year is 364 days long, split into thirteen months, each of which has exactly four weeks. Furthermore, each week starts on a Monday, implicating that each month starts on a Monday as well.

The primary advantages of this calendar system are the ease of calculating the day of the week and the ability to reuse the same calendar for every year. It also eliminates the need to calculate the date for holidays that are determined by the day of the week (e.g. the last Monday of November).

However, it also presents a major drawback: since thirteen is a prime number, the year could not be divided into segments such as halves or quarters, which are commonly used in business planning. To this end, I introduced a slight redesign to the calendar system, which was the inversion of the weeks and months.

The dates

Instead of having thirteen months, silican dates have four seasons, each of which has thirteen weeks, which have seven days, as before. The numerical format of silican dates is: <year>/<season>/<week>/<day of week>. Thus, today's date would be .

The leap years are calculated by a rule similar to that of the Gregorian calendar: a year is a leap year when it is divisible by five or 400, but not fifty. Leap years have an extra week (the fourteenth week) in the last quarter.

Just for my own entertainment, I've given each of the seasons, weeks, and days of the weeks a name in my own constructed language, Naidira. The names for the days of the week are derived from the names of gemstones, and the names for the seasons and weeks were created specifically for this calendar (i.e. they have no other meanings). Of course, if this calendar system does become prevalent, I don't expect these names to be actually used by others.

Number Season Week Day of the week
1 Nevari Ateluna Boromika (amethyst)
2 Penari Beviruto Ferimanika (pink onyx)
3 Sevari Deruna Lusinika (lapis lazuri)
4 Venari Elito Navimilka (ruby)
5 Feridina Perinatika (amber)
6 Geranito Relikanika (emerald)
7 Lunamarina Temiranika (obsidian)
8 Miraliluto
9 Peridina
10 Samerito
11 Timina
12 Verato
13 Wilaluna
(14) Zeroto


This adjustment stems from the fact that months no longer track the orbital period of the moon, and presently, they are rather arbitrary subdivisions of the year, which produce uneven quarters (the first quarter is always the shortest due to February having the fewest days).

Eight-hour clock

Accompanying the calendar, I also created a slightly different clock to represent the time of the day. As the name suggests, the eight-hour clock splits the day into three eight-hour periods, which start at midnight (0:00 or 12 AM), 8:00 (8 AM), and 16:00 (4 PM).

Like the dates, I also created names for the three periods of the day in my now-defunct language, Menteia.

Period name Corresponding time
Valima (night) 0:00–7:59 (12 AM to 7:59 AM)
Derina (day) 8:00–15:59 (8 AM to 3:59 PM)
Geluna (evening) 16:00–23:59 (4 PM to 11:59 PM)

The format I use for eight-hour time is <period><hour><minutes>. Thus, 11:37 would be D337. This division of the day also means that noon occurs at D400, which is exactly at the middle of the day period (thus, "mid-day").


This division reflects the different periods of everyday life, which can be roughly split into thirds, namely, work/study, recreation, and sleep.