Possible bug in skyfield (new almanac module)

[Tomasz Lewicki]

Dear group.

Yesterday I upgraded two of my three stations to Weewx 5.2 and encountered strange problem (bug?) with new almanac module. On first glance everything works good, data are presented as before but I've noticed that moonrise is incorrectly calculated. I use timeanddate.com to check my calculations. I provide data for one of the two stations from Weewx 5.2, as they are located approximately 3 km apart.

Now the numbers:

Station 1: latitude = 50.70737, longitude = 16.22252. Weewx 5.2 with weewx-skyfield-almanac installed and enabled shows for today (15.10.2025) moonrise at 01:20:49, moonset at 16:10:39. Station 2, approx. 20 km NE from station 1. Weewx 5.2 with weewx-skyfield-almanac installed and enabled shows for today (15.10.2025) moonrise at 01:19:32, moonset at 16:10:19. timeanddate.com for nearby bigger city (approx. 10 km north) shows accordingly 00:00 and 16:10. Culmination, sunrise and sunset are OK for both stations.

Third station cannot be upgraded because OS there couldn't find source for python3-skyfield module and this station is still working with Weewx 5.1 and PyEphem. Moonrise and moonset for this location are as follows: 00:00:07 and 16:10:38 - and this is correct.

I'm sure that for station 1 and 2 (Weewx 5.2) skyfield module does the calculations because solstices and equinoxes are perfectly equal up to single second but third station (Weewx 5.1 and PyEphem) shows differences of a few seconds.