Ishtar is [[Venus?]] in another universe where the sun’s light is dimmer. Why this is so exactly, does not concern the present story, though it is a factor in what happens. Venus is a time keeper’s nightmare and a timekeeper’s dream. It’s axis does not process, it’s axis is only slightly inclined to its ecliptical plane, it has no moon to create eccentricities in its rotation, it’s orbit is more circular than Earth. In short, it is a paragon of regularity. For this same reason, it offers few long term features of time. It has no moon to give it months, very weak seasons, making the solar year a less compelling period than on Earth, and it if it were a habitable planet, it would have a large ocean to regulate climate.
However, as the story makes clear, the Ishtari did not evolve on that world, but were brought there from elsewhere. That elsewhere is Earth, and thus their oldest calendar, which is the main one used both in the story and through out their world is the “Long Count” which keeps track of Earth very closely.
The form is based on a [[Maya | Mayan]] type calendar, using the synodic period of Earth as the “long counter” of years. The Mayans followed Venus through the sky closely, and built it into their date system. The Long Count of Ishtar is similar, with 13 venusian years – here called “[[annae?]]” forming one long count. The long count date then is (13’s of annae).(annea remainder).(days). The Isthari think of one turning of the Long Count in a manner similar to the way we think of decades, and the tens as like a century. In short hand they often do not notate the first digit at all, though scholars and others that understand history do. The turning of the hundred’s place is a millennial event, since roughly 800 Earth years pass between such events. As with earth, the approaching of a millennium is viewed with alternate hope and religious implication, and theirs is, to their mind, an increasing presence, the way 2000 was in our year 1990.
The year zero is, as is made clear, very far back in the past, farther back than any existing civilization of Ishtar, and no one truly knows what the reason for the date was, or the selection of 13 years, except that it coincides with the period of Earth in the famous 13:8 ratio. Almost.
For the length of the Venusian day I took the original spin of Venus, assumed that it had formed retrograde, and applied the tidal draf of the sun on its oceans, the result was a bit over 19 hours, which I shortened to being an exact multiple of the year, since the error of the calculation permitted it, and “tidal locking” would probably encourage it. This yields a Venusian hour – dividing the sky into 24 parts – of 46 minutes. In our universe the thick Venusian atmosphere has created tidal drag that has slowed the planet down to having a rotational period of 243 solar days. Terraformers of our Venus will have problems with daylight an an acute hydrogen shortage, as well as the lack of a magnetic field, to deal with. Ishtars have a magnetic field from a faster spinning planet – and more displays of the aurora that go farther over the planet.
As for the rest of the oddities, that is, truly, the subject of the novel, and cannot be explained in any greater depth without giving away various important aspects of what the characters will discover.