Winter solstice

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The winter solstice (the solstice term comes from the Latin sun ["Sun"] and sistere ["remain still"]; also, hyemal solstice) corresponds to the instant that the position of the Sun in the sky is at the greatest negative angular distance from the celestial equator. Depending on the correspondence with the calendar, the winter solstice event takes place between 21 and 22 December each year, in the case of the northern hemisphere, and between 20 and 21 June, in the case of the southern hemisphere. This variation is due to the time lag caused by the leap years.

Development
The seasonal meaning of the winter solstice is manifested in the reversal of the tendency to extend the duration of the nights and shorten the hours of the day. Different cultures define this in different ways, as it is sometimes considered that, astronomically, it can point to either the beginning or half of the winter of the hemisphere. The word winter has a subjective meaning, since it does not have a principle or half that is scientifically established; however, in the case of the winter solstice, it is possible to calculate exactly the second in which it occurs. Although in theory the winter solstice only lasts a moment, this term is also usually used to refer to the 24 hours of the day it takes place.

The meaning or interpretation of this event has varied in the different cultures of the world, but most of them recognize it as a period of renewal and rebirth, involving festivals, fairs, meetings, rituals or other celebrations.

Date

In the Julian calendar, 25 December was established as the winter solstice of Europe. There was a difference between the calendar year (365,2500 days) and the tropical year (365,2422 days), and that difference caused the astronomical solstice not to always fall on the same day, but to advance approximately three days every four centuries. In 1582, Pope Gregory XIII decreed the change to the new Gregorian calendar, making the winter solstice (in the northern hemisphere) happen around December 21. In the Gregorian calendar, solstice fluctuates slightly, but in the long term (only about one day every 3000 years).

The figures on the left show the differences between the Gregorian calendar (Figure 1: use of 1 leap year every 4 years) and the Persian calendar jalali (Figure 2: using the arithmetic of 33 years approach), in reference to the time of the year the "winter," you have the solstice of December. The Y-axis represents the "days of error" and the X-axis shows the years of the Gregorian calendar. Each point represents a single date in a given year. The error per cycle is approximately 1 day every 4 years, and is corrected with one leap year every four years regularly and, in the case of the Persian calendar also a leap period