Winter solstice one must be able to observe a change in azimuth or elevation less than or equal to about 1/60 of the angular diameter of the sun. Observing that it occurred within a two-day period is easier, requiring an observation precision of only about 1/16 of the angular diameter of the sun. Thus, many observations are of the day of the solstice rather than the instant. This is often done by observing the sunrise and sunset or using an astronomically aligned instrument that allows a ray of light to be cast on a certain point around that time. Length of day
Saint Lucy's Day was created on Spring equinox (thought to fall on 25 March at the time), and that Christ had been conceived on that date, being born 9 months later on Winter solstice. A Swedish source states that the date of (Winter Solstice, St. Lucia, Lucinatta, Lucia-day, Lussi-mass ...) i.e. 13 December, predates the Gregorian which implies that "Lucia's Day" "was" 13 Dec in the Julian Calendar, "which is equal to" 21 December in the Gregorian, i.e. now. Same source states use of the name "Little Yule" for the day, that it was among the most important days of the year, that