This is a calendar question, for the Fortnightly Topic.
On planet Polarworld, a future alternate Earth, the ambient temperatures are so intense that the only habitable areas are at the poles.
Now for reasons that almost certainly aren’t relevant to this question, this situation was not always thus. In other words, Once Upon A Time in the Time Of Legends, the poles were frigid, inhospitable wastes, and people lived in the areas in between. Over the many millennia since The Time Of Legends, people have migrated to the two poles.
Technologically, these two civilizations are about as far forward as early modern Europe, say somewhere from 1450-1700—except that their abilities in navigation are minimal, because the oceans are so horrible that there isn’t a lot of deep-sea exploration undertaken. One interesting result is that these two civilizations have effectively no knowledge of each others’ existence. So far as each knows, their people were the only ones to survive by migrating far to the pole.
Well, eventually these folks independently discover the principles of radio (not at precisely the same time, of course), and soon enough discover each other. Once basic language problems and such are resolved, they start trying to share knowledge about their mutual history—and discover a major problem in the form of the calendars.
Northpole society and Southpole society have quite distinct calendars, naturally. The real problem, once they start talking to one another, is that these calendars don’t readily align with one another. Some factors in this:
Each society has its own night sky.
Seasons are exactly reversed.
There are long periods (the high summers) when celestial observations are very difficult because the sun is always up.
You will of course recognize many others.
The Southpole calendar centers around precise observation of glacial calving. As the seasons drift toward summer, a bit after the vernal equinox, a few major glaciers will calve. This is watched and measured with intense care and precision. When the experts judge the time to be correct (when a certain exact amount of calving has been completed), then at that precise instant the Calvendar [har har] is held to have begun for the year. The Calvendar ends at midnight on the vernal equinox. Between the equinox and the calving is an intercalary time during which everyone hides in their cities and parties hard to drive off the spirits of darkness.
The Northpole calendar does everything on the basis of celestial observations, with a strong preference for observations of Venus (since she can often be seen even when the sun is up). They have become extremely precise about their celestial observations, and can predict the arrival of long-range recurrent phenomena (Halley’s comet, for instance) with enormous accuracy. They consider that the year always begins at the moment of summer solstice, which they calculate and observe very precisely. But they also know that the Earth year is 365.24 days (8765 hours), and they hold that earthly observations are inevitably false. Therefore, their calendar doesn’t put day and night in the same place all the time. They divide everything into 5 Great Months of 1753 hours each. For convenience’s sake, these are cut into 56 Days of 31 hours each. Between the first and the second Little Months of 28 Days each comes a Starday of 17 hours, during which great festivals are held in honor of the various Star Spirits (this is especially exciting when Venus can be seen during a Starday). Of course, it is true that one cannot look at one’s watch, see that it’s “noon,” and on this basis assume anything whatever about whether the sun is up or not, but that’s sort of true anyway if you’re living at the pole.
How might the Northpole and Southpole calendars be reconciled to one another with minimal transformation?
Note: A mere translation is a matter of doing the math and spending a lot of time with the Southpolers’ calving charts. But now that they’ve realized that they’re All One Human Society Together and so forth, they’d like to have a single calendrical system that respects both traditions. So how could that work?