They differ due to the variation in the solar day throughout the year caused by the Earth's elliptical orbit (see: earliest and latest sunrise and sunset).

Several proposals exist, a commonly mentioned one connecting it to the Proto-Indo-European root *wed- 'water' or a nasal infix variant *wend-.

[1] The tilt of the Earth's axis relative to its orbital plane plays a large role in the formation of weather.

During winter in either hemisphere, the lower altitude of the Sun causes the sunlight to hit the Earth at an oblique angle.

The manifestation of the meteorological winter (freezing temperatures) in the northerly snow-prone latitudes is highly variable, depending on elevation, position versus marine winds, and the amount of precipitation.

For instance, within Canada (a country of cold winters), Winnipeg, on the Great Plains (a long way from the ocean), has a January high of −11.3 °C (11.7 °F) and a low of −21.4 °C (−6.5 °F).

[2] In comparison, Vancouver, on the west coast (with a marine influence from moderating Pacific winds), has a January low of 1.4 °C (34.5 °F), with days well above freezing, at 6.9 °C (44.4 °F).

A similar but less extreme effect is found in Europe: despite their northerly latitude, the British Isles have no non-mountain weather stations with a below-freezing mean January temperature.

[8] The Swedish Meteorological Institute (SMHI) defines thermal winter as when the daily mean temperatures are below 0 °C (32 °F) for five consecutive days.

[10][11] Accumulations of snow and ice are commonly associated with winter in the Northern Hemisphere, due to the large land masses there.

[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.

[18] In many countries in the Southern Hemisphere, including Australia,[19][20] New Zealand,[21] and South Africa, winter begins on 1 June and ends on 31 August.

[22] In Chinese astronomy and other East Asian calendars, winter is taken to commence on or around 7 November, on Lìdōng, and end with the arrival of spring on 3 or 4 February, on Lìchūn.

[27] The hibernal season coincides with the main period of biological dormancy each year whose dates vary according to local and regional climates in temperate zones of the Earth.

The appearance of flowering plants like the crocus can mark the change from ecological winter to the prevernal season as early as late January in mild temperate climates.

Larger plants, particularly deciduous trees, usually let their upper part go dormant, but their roots are still protected by the snow layer.

[33][34] In Persian culture, the winter solstice is called Yaldā (meaning: birth) and has been celebrated for thousands of years.