The Winter Solstice occurs exactly when the earth's axial tilt is farthest away from the sun at its maximum of 23° 26'. Though the Winter Solstice lasts an instant in time, the term is also colloquially used like Midwinter to refer to the day on which it occurs. For most people in the high latitudes this is commonly known as the shortest day and the sun's daily maximum position in the sky is the lowest. The seasonal significance of the Winter Solstice is in the reversal of the gradual lengthening of nights and shortening of days.
Worldwide, interpretation of the event has varied from culture to culture, but most cultures have held a recognition of rebirth, involving holidays, festivals, gatherings, rituals or other celebrations around that time.
Since 45 BCE, when the 25th of December was established in the Julian calendar as the winter solstice of Europe, (Latin: Bruma), the difference between the calendar year (365.2500 days) and the tropical year (365.2422 days) moved the day associated with the actual astronomical solstice forward approximately three days every four centuries until 1582 when Pope Gregory XIII changed the calendar bringing the northern winter solstice to around December 21. Yearly, in the Gregorian calendar, the solstice still fluctuates slightly but, in the long term, only about one day every 3000 years.For Celtic countries, such as Ireland, the calendarical winter season has traditionally begun November 1 on All Hallows or Samhain. Winter ends and spring begins on Imbolc or Candlemas, which is February 1 or 2.The winter solstice may have been immensely important because communities were not certain of living through the winter, and had to be prepared during the previous nine months. Starvation was common in winter between January and April, also known as the famine months. In temperate climates, the midwinter festival was the last feast celebration, before deep winter began. Most cattle were slaughtered so they would not have to be fed during the winter, so it was almost the only time of year when a supply of fresh meat was available. The majority of wine and beer made during the year was finally fermented and ready for drinking at this time.
Meán Geimhridh (Irish tr: midwinter) or Grianstad an Gheimhridh (Ir tr: winter solstice) is a name sometimes used for hypothetical midwinter rituals or celebrations of the Proto-Celtic tribes, Celts, and late Druids. In Ireland's calendars, the solstices and equinoxes all occur at about midpoint in each season. The passage and chamber of Newgrange (Pre-Celtic or possibly Proto-Celtic 3,200 BCE), a tomb in Ireland, are illuminated by the winter solstice sunrise. A shaft of sunlight shines through the roof box over the entrance and penetrates the passage to light up the chamber. The dramatic event lasts for 17 minutes at dawn from the 19th to the 23rd of December. The point of roughness is the term for the winter solstice in Wales which in ancient Welsh mythology, was when Rhiannon gave birth to the sacred son, Pryderi.