[Warning: math nerd ramble ahead.]
So for a long time I've been vaguely obsessed with the question of Avaria's moons. Moonless nights are an important little detail for Kamenes, and I thought it'd be a delightful side project (yes, I am a statistician, how did you guess) to build a lil' moon calculator spreadsheet.
But the more I looked into this question, the more perplexed I got. Ostensibly, Niota has a 14-day cycle and Celeiri a 28-day one. This would make the eight phases of the moon last around 1.75 days each for Niota, and 3.5 for Celeiri. But more importantly it'd put the rhythm of their cycles in lockstep - either every time Celeiri was new Niota would also be, or they'd NEVER coincide. That clearly wasn't happening with even a cursory glance at my logs. And while Niota seemed fairly right for a 14-day cycle, Celeiri's cycle also seemed crazy long - since I started looking at the moons most every day early in August, I definitely had stretches of observing the same phase for Celeiri for like a solid week at a time.
Cue the activation of a certain flavor of mystery-solving hyperfixation I share with my character. And roughly three months' worth of log data later, I think I have figured out what's going on!
There are indeed eight phases of the moon, but there are four general 'stages' - waxing and waning crescent, waxing and waning gibbous. The other phases (new, first quarter, full, and third quarter) are subsumed in these four stages. IRL, each stage lasts ~7.38 days to net you a roughly 29.5-day cycle. What I think has happened with Celeiri is that it is coded to have all EIGHT phases receive a roughly 7.38 day duration instead of all FOUR stages, resulting in a ~59-day cycle instead of a 28-day one. Now this could be anywhere from 56 days to 59 in reality, but my moon observations would make a phase length between 7-8 hours more plausible than a strict, exact 7... and a 59-day cycle would explain the offset between Celeiri and Niota better than a 56-day one.
To confirm, I checked my logs to determine I saw Celeiri full on 6/15 and 6/16- a new moon around 7/18 - then full again on 8/12 and 8/13. 58 days apart, give or take some unknown number of hours! (Note: the 7-8 days for full include descriptors like 'barely short of full', I think, so getting a straight-up 'full' means being fairly localized to the same time in each cycle.)
...I do realize that I could have just shot Pilgrim a DM and asked how the moons were coded, but 1) I do not wish to unnecessarily pester our lovely vagrant and 2) I love excuses to make spreadsheets. That said, Pilgrim, if you're reading this I'd loooove to know the exact timing data so I could make a Moon Calculator, purely for my own personal satisfaction since for all RP purposes it almost certainly makes sense to handwave things.
TL;DR: Celeiri funny, me too.