The first day of winter observances: Samhain in the Northern Hemisphere and Beltane in the Southern Hemisphere, celebrations start at sunset of October 31 (Neopagan Wheel of the Year)

Samhain or Sauin is a Gaelic festival on 1 November marking the end of the harvest season and beginning of winter or the "darker half" of the year. It is also the Irish and Scottish Gaelic name for November. Celebrations begin on the evening of 31 October, since the Celtic day began and ended at sunset. This is about halfway between the autumnal equinox and winter solstice. It is one of the four Gaelic seasonal festivals along with Imbolc, Bealtaine, and Lughnasa. Historically it was widely observed throughout Ireland, Scotland, and the Isle of Man. Its Brittonic Celtic equivalent is called Calan Gaeaf in Wales.

The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the Solar System as Earth's North Pole.

Beltane or Bealtaine is the Gaelic May Day festival, marking the beginning of summer. It is traditionally held on 1 May, or about midway between the spring equinox and summer solstice. Historically, it was widely observed in Ireland, Scotland, and the Isle of Man. In Ireland, the name for the festival in both Irish and English is Lá Bealtaine. In Scottish Gaelic it is called Là Bealltainn, and in Manx Gaelic Boaltinn or Boaldyn. It is one of the four main Gaelic seasonal festivals—along with Samhain, Imbolc, and Lughnasadh—and is similar to the Welsh Calan Mai.

The Southern Hemisphere is the half (hemisphere) of Earth that is south of the equator. It contains all or part of five continents and four oceans, as well as New Zealand and most of the Pacific Islands in Oceania. Its surface is 80.9% water, compared with 60.7% water in the Northern Hemisphere, and it contains 32.7% of Earth's land.