Colonial calendar
Humans have an urge to keep track of the passing of time, either the time of the day, the day of the year, or which year it is, and have come up with many ways of keeping track of time on Earth and various units of time. The prevailing one, the hour, has served well for the past thousand-odd years, but the familiar 24 hour day cannot be used on Poseidon unless the hour is lengthened. The day of Poseidon is just over 30 hours and there are 330 days in a year and the original Athena Project colonists simply created a modified military custom of defining the time and the date.
The time of the day is noted as hhmm or 29:45 for a quarter to midnight and the date is noted as ddd.yy where yy is the year counted since Planetfall, hence the notion 45 SP when a specific year is intended, and ddd is the day within the year. E.g. 063.99 is the 63rd day of the 99th year since Planetfall. See Player's Guide (BPv2) p 226 for details.
As the Poseidon year is a fraction under 330½ days, leap years occur more often than on Earth. The rule is:
- If the year divided by 7 has remainder 1, 3, or 5, the year is a leap year (331 days)
- Other years are not leap years (330 days)
Other, archaic, units of time are still used. The week is still defined to be seven days, and the month is defined as 30 days.
As for how Poseidoners spend their 30-hour days, another page describes the rhythm of a day on Poseidon.
Converting dates
We have pages to convert CE dates to colonial and convert colonial dates to CE.
You can see the code that drives this conversion.
See also Bluedive's date converter.
Significant dates
For a complete timeline from 1957 until present day (2199), see Player's Guide (BPv2) pp 237-252. The following is a brief colonial calendar for reference.
| Colonial Date | CE Date | Event |
|---|---|---|
| 001.0 | 3 January 2087 | Planetfall |
| 150.09 | September 2097 | Abandonment recognised |
| 076.33 | 7 August 2124 | Volcanic cataclysm destroys Atlantis |
| 52 | 2146 | Fire destroys fusion reactor in Haven |
| 163.69 | 15 August 2165 | Recontact: The arrival of UNSS Adm. Robert Perry |
| 76 | 2172 | The arrival of UNSS Ballard, with additional supplies |
| 88 | 2187 | Start of the Long John rush |
| 001.99 | 2 January 2199 | First day of Now |
| 331.99 | 18 February 2200 | Last day of Now |
Astronomical periods
| Siderial | Synodic | |
| Day length | 29 h, 55 m, 18 s | 30 h, 0 m, 43 s |
| Proteus "month" | 1166 h, 47 m, 25 s | 43 d, 26 h, 51 m, 50 s |
| Nereus "month" | 1942 h, 06 m, 19 s | 80 d, 03 h, 11 m, 2 s |
| Length of year | 9916 h, 48 m | 330 d, 13 h, 2 m, 17 s |
(Siderial times are taken relative to the fixed stars; synodic (and solar) times are taken relative to the position of the sun overhead. Syndoic times are given in terms of local (solar) days. I assume that the periods in the BP books are synodic, so make sense for an observer on Poseidon timing the period from noon to noon.)