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Very easy for the calendar itself. Referencing something like this: https://elderscrolls.fandom.com/wiki/Calendar would let you copy/paste the months/days names in and then a bit of work to set up the events, which are blessedly broken down per month (love that), the moons you'd need to do a bit of guesswork for - there's no lore that I know of (nor that I can find when I double checked my own memory) that specifically talks about their phases, but we do get told that there are several eclipses per year (https://en.uesp.net/wiki/Lore:Moons here) so I'm sure someone who knows lunar phases better could work that out with a bit of math! (or you could make up a 'close enough' approximation fairly quickly)