Writers of historical fiction set before the advent of gas and electrical lighting should be aware of how daylight and moonlight (including sunrise and sunset times, moon phases, and the like) should affect their story.

* Writers from the southern US often forget that most of Europe and especially the UK is pretty far north compared to where they live, being more on a line with western Canada than the US. This difference doesn’t affect the weather (due to the Gulf Stream) as much as it does the balance of day and night; on 21 June in London, to give an example, dawn breaks at 2:55 AM standard time (they didn’t have daylight saving time until after electric lights existed) and the sun rises at 3:42 AM. On 21 December, on the other hand, dawn breaks at 7:23 AM and the sun rises at 8:03 AM. Days in late June are 16 ½ hours long: days in late December are less than 8 hours long. That difference affects everything from when characters breakfast and dine to when they entertain to how much they must budget for candles to how much natural light they have if they awaken in the middle of the night. The difference is starker in Scotland, Muscovy, or Scandinavia; no one in Peter the Great’s St. Petersburg who woke up at 3 AM in June had two hours to wait for dawn. At that latitude, it’s dawn all night long.

* Country activities held at night such as assemblies, political meetings, and private parties/balls were often tied to the phase of the moon, especially in autumn, winter, and spring. In Pride and Prejudice, Bingley takes possession of Netherfield on Michaelmas (29 September) and almost immediately rushes off to fetch Darcy and his sisters and brother-in-law so they can attend the Meryton Assembly the evening they arrive. This makes a beginning date for P&P of 29 September 1811 plausible, since the full moon in that year fell on 2 October. Your characters are therefore going to know what the moon phase is at all times and plan activities around it.

* They’ll also know where the moon is supposed to be in the sky, as will a large percentage of your readers. The writer who puts a rising crescent moon in the eastern sky in early evening or a full moon low at the horizon at midnight is going to disrupt suspension of disbelief for every astronomy fan who reads their book, in the same way as calling a knight or baronet “Sir Surname” will disrupt suspension of disbelief for history fans.

* Nobody in the 18th century thought eclipses were a sign of the end of the world. Eclipses were understood by this time, even by the common people.