874
xkcd #2897: Light Leap Years
(imgs.xkcd.com)
Alt text:
When Pope Gregory XIII briefly shortened the light-year in 1582, it led to navigational chaos and the loss of several Papal starships.
idk, it feels more intuitive for it to be based on the mode (most common) year length (365) instead of the average year length (365.2425).
The boring answer is that in physics a year is just defined as the time it takes for the Earth to orbit the sun, they don't care about calendars and leap years