Astronomical and other calendar-based reckoning

Astronomical and other calendar-based reckoning

In the mid-latitudes and polar regions, winter is associated with snow and ice.

In the Southern Hemisphere winter extends from June to September, pictured in Caxias do Sul in the southern highlands of Brazil.

Sea ice in the Port of Hamburg, Germany
In the Northern Hemisphere, some authorities define the period of winter based on astronomical fixed points (i.e. based solely on the position of the Earth in its orbit around the Sun), regardless of weather conditions. In one version of this definition, winter begins at the

winter solstice and ends at the March equinox.[12] These dates are somewhat later than those used to define the beginning and end of the meteorological winter – usually considered to span the entirety of December, January, and February in the Northern Hemisphere and June, July, and August in the Southern.[12]

Astronomically, the winter solstice, being the day of the year which has fewest hours of daylight, ought to be in the middle of the season,[13][14] but seasonal lag means that the coldest period normally follows the solstice by a few weeks. In some cultures, the season is regarded as beginning at the solstice and ending on the following equinox[15][16] – in the Northern Hemisphere, depending on the year, this corresponds to the period between 20, 21 or 22 December and 19, 20 or 21 March.[12]