The way the sun and the moon are represented got me thinking about when solar eclipses might have been visible in the years of the game. I found these PDFs https://eclipse.gsfc.nasa.gov/SEpubs/5MCSE.html
And I think this one is the one for URW: https://eclipse.gsfc.nasa.gov/5MCSE/5MCSE-Maps-08.pdf
While there is nothing with textual material, for a richer experience one could use software these days; two are referenced below although I'm sure there are many others.
Software can help simulate position on earth and then look up to the virtual sky to see celestial body positions, including but not limited to Sun and Moon.
These type of simulations, even those that let you change date & time probably won't go back to Iron Age Finland but we are in the game-level simulation domain anyway - scientific-level simulation correctness is probably unnecessary here.
First software is free, the other one is commercial (no affiliation) but strongly recommended to anyone with an interest in astronomy - it's the lego of stars.
EDIT: I forgot to say, if one is mildly interested but can't be bothered to download & install, there is a web version, here:
https://stellarium-web.orgStellarium"Stellarium is a free open source planetarium for your computer. It shows a realistic sky in 3D, just like what you see with the naked eye, binoculars or a telescope."
https://stellarium.orgUniverse Sandbox"Universe Sandbox is a physics-based space simulator. It merges gravity, climate, collision, and material interactions to reveal the beauty of our universe and the fragility of our planet. Create, destroy, and interact on a scale you've never before imagined. Rated Overwhelmingly Positive from over 11,000 Steam reviews."
https://universesandbox.comJust fired up Stellarium & took a screenshot, just to give an idea: