Anarresti Calendar and Clock

The Anarresti day is about 25 Earth hours. This can vary because Anarres forms a dual planet system with Urras. Anarres has two years: the Sun year (aFas Vosterry) (the time for Urras and Anarres to go around the Sun, Tau Ceti, about 344 Anarresti days) and the Anarres year (aFas Narresy) (the time taken for Anarres and Urras to orbit their common centre of mass, about 56 Anarresti days). There are two words for day: Las, the period from sunrise to sunrise; and Hisk, the opposite of night (Mesh).

The Anarresti week (Decad) has ten days. The days are:

Dates are usually recorded as [year]/[decad number]/[day number]. So the eighth day of the 23rd Decad of the year 172 would be 172/23/8 (Nivenes/Nenat/Vat). Where a Decad covers two years it is dated into the earliest year.

There is a thirty-five year cycle (KLas), at the end of which the Sun year, the Anarres year and the Decad are considered to be back in line. There may be some "non-days" added to the calendar to make the alignment as astronomically correct as possible. These are treated as extra community activity days.

The Annaresti day is divided into 24 roughly equal periods (Anarresti "hours", Horri aNarresy). A fairly typical day would be:

Because Anarres is orbiting Tau Ceti as a dual planet system with Urras, the day length can be variable. To deal with this, the clock is reset each day so that the 13th hour begins when the sun is at its highest in the sky. However, Anarres does not have the "time is money" mentality of capitalist and managed economies, so nobody is tied to anyone else's schedule (or to the clock) except by agreement.

Anarres has many traditions, holidays and festivals throughout the year, the chief of which is Insurrection Day (Las niPygvaty greVoki), which is also the midsummer festival.

Anarres and Urras are orbiting each other at an angle of ±2° from the ecliptic, so eclipses happen several times in a Sun year - they are common events.