Editing Winter (section)

==Astronomical and other calendar-based reckoning==
[[File:KleinarlWinterwonderland.jpg|thumb|In the [[mid-latitudes]] and [[Polar regions of Earth|polar regions]], winter is associated with snow and ice.]]
[[File:Neve Caxias do Sul (2).jpg|thumb|In the [[Southern Hemisphere]], winter extends from June to September, pictured in [[Caxias do Sul]] in the southern highlands of [[Brazil]].]]
[[File:Hamburg Germany Jan 6.jpg|thumb|[[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]].<ref name=":0">{{Cite web|url=http://www.ncei.noaa.gov/news/meteorological-versus-astronomical-seasons|title=Meteorological Versus Astronomical Seasons|date=September 22, 2016|website=National Centers for Environmental Information (NCEI)|language=en|access-date=2019-12-28}}</ref> 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.<ref name=":0" /><ref>{{Cite web|title=When does winter start?|url=https://www.metoffice.gov.uk/weather/learn-about/weather/seasons/winter/when-does-winter-start|access-date=2021-10-11|website=[[Met Office]]}}</ref>

Astronomically, the winter solstice — being the day of the year that has fewest hours of daylight — ought to be in the middle of the season,<ref>{{cite book|last=Ball|first=Sir Robert S|title=Elements of Astronomy|year=1900|publisher=The MacMillan Company|location=London|page=[https://archive.org/details/elementsastrono02ballgoog/page/n74 52]|url=https://archive.org/details/elementsastrono02ballgoog|isbn=978-1-4400-5323-8}}</ref><ref>{{cite book|last=Heck|first=Andre|title=Organizations and strategies in Astronomy Volume 7|year=2006|publisher=Springer|isbn=978-1-4020-5300-9|page=14|url=https://books.google.com/books?id=YSsaxkeixH0C&pg=PA14}}</ref> 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]].<ref>{{cite encyclopedia | url=https://www.britannica.com/science/winter |title=winter |date=16 September 2022 |encyclopedia=Encyclopædia Britannica |access-date=28 October 2022}}</ref><ref>{{cite encyclopedia |url=https://www.britannica.com/science/solstice |title=solstice |encyclopedia=Encyclopædia Britannica |access-date=28 October 2022}}</ref> 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.<ref name=":0" />

In an old Norwegian tradition, winter begins on 14 October and ends on the last day of February.<ref>{{cite web|url=http://met.no/./?module=Articles;action=Article.publicShow;ID=1104 |title=Første vinterdag |language=Norwegian |archive-url=https://web.archive.org/web/20110629191011/http://met.no/?module=Articles;action=Article.publicShow;ID=1104 |archive-date=29 June 2011 |date=14 October 2008 |website=The Norwegian Meteorological Institute |access-date=31 August 2009}}</ref>

In many countries in the [[Southern Hemisphere]], including [[Australia]],<ref>{{cite dictionary|url=http://www.bom.gov.au/climate/glossary/seasons.shtml |dictionary=Meteorological Glossary |title=Seasons |archive-url=https://web.archive.org/web/20090307042010/http://www.bom.gov.au/climate/glossary/seasons.shtml |archive-date=7 March 2009 |access-date=21 June 2009 |url-status=live |publisher=Australian Bureau of Meteorology}}</ref><ref>{{cite web |last=Hamilton |first=Daniel |url=http://www.abc.net.au/local/photos/2009/06/02/2583319.htm |title=Images from around Australia on first day of Winter 2009 |publisher=Abc.net.au |date=2 June 2009 |access-date=23 May 2012 |url-status=live |archive-url=https://web.archive.org/web/20121112213348/http://www.abc.net.au/local/photos/2009/06/02/2583319.htm |archive-date=12 November 2012 |df=dmy-all }}</ref> [[New Zealand]],<ref>{{cite news |last1=Deguara |first1=Brittney |title=When does winter officially start in New Zealand? |url=https://www.stuff.co.nz/national/113038178/when-does-winter-officially-start-in-new-zealand |work=Stuff |date=27 May 2019 |access-date=4 October 2020}}</ref> and [[South Africa]], winter begins on 1 June and ends on 31 August.

In [[Celtic nations]] such as Ireland (using the [[Irish calendar]]) and in Scandinavia, the winter solstice is traditionally considered as midwinter, with the winter season beginning 1 November, on [[Halloween|All Hallows]], or [[Samhain]].{{cn|date=September 2023}} Winter ends and spring begins on [[Imbolc]], or [[Candlemas]], which is 1 or 2 February.<ref>{{cite news|url=https://www.irishpost.com/news/today-marks-the-first-day-of-spring-on-the-gaelic-calendar-202700|title=Today marks the first day of spring on the Gaelic calendar|first=Rachael|last=O'Connor|date=1 February 2021|website=[[The Irish Post]]}}</ref> In [[Chinese astronomy]] and other East Asian [[Chinese calendar|calendars]], winter is taken to commence on or around 7 November, on [[Lidong|Lìdōng]], and end with the arrival of spring on 3 or 4 February, on [[Lichun|Lìchūn]].<ref name="chinafetching">{{cite web |url= https://www.chinafetching.com/24-solar-terms-in-chinese-calendar |title= 24 Solar Terms in Chinese Calendar|author=<!--Not stated--> |date= |website= ChinaFetching.com|publisher= |access-date= |quote=}}</ref> Late [[Roman Republic]] scholar [[Marcus Terentius Varro]] defined winter as lasting from the fourth day before the [[Roman calendar#Days|Ides]] of [[November (Roman month)|November]] (10 November) to the eighth day before the Ides of [[Februarius]] (6 February).<ref name="Varro37BC">{{cite wikisource |author=Varro |author-link=Varro |title=Res Rusticae (Country Matters) |volume=Book 1 |orig-date=c. 37 BCE |plainchapter=4 Concerning the Agricultural Seasons}}</ref>

This system of seasons is based on the length of days exclusively. The three-month period of the shortest days and weakest solar radiation occurs during November, December and January in the Northern Hemisphere and May, June and July in the [[Southern Hemisphere]].

Many mainland European countries tended to recognize [[Martinmas]] or [[St. Martin's Day]] (11 November) as the first calendar day of winter.<ref>{{Cite book|url=https://books.google.com/books?id=rYT8MPFl_egC&pg=PA219|title=Folk-Taxonomies in Early English|last=Anderson|first=Earl R.|publisher=Fairleigh Dickinson University Press|year=2003|isbn=978-0-8386-3916-0|location=Madison, N.J.|pages=219|quote="On St. Martin's day (11 November) winter begins, summer takes its end, harvest is completed. ...This text is one of many that preserves vestiges of the ancient Indo-European system of two seasons, winter and summer."}}</ref> The day falls at the midpoint between the old Julian equinox and [[solstice]] dates. Also, [[Valentine's Day]] (14 February) is recognized by some countries as heralding the first rites of spring, such as flowers blooming.<ref>{{Cite book|last1=Glick|first1=Thomas F.|url=https://books.google.com/books?id=hr62AgAAQBAJ&q=science+first+day+of+winter&pg=PT353|title=Medieval Science, Technology, and Medicine: An Encyclopedia|last2=Livesey|first2=Steven|last3=Wallis|first3=Faith|date=2014-01-27|publisher=Routledge|isbn=978-1-135-45939-0|language=en}}</ref>

The three-month period associated with the coldest average temperatures typically begins somewhere in late November or early December in the Northern Hemisphere and lasts through late February or early March. This "thermological winter" is earlier than the solstice delimited definition, but later than the daylight (Celtic or Chinese) definition. Depending on [[seasonal lag]], this period will vary between climatic regions.

Since by almost all definitions valid for the Northern Hemisphere, winter spans 31 December and 1 January, the season is split across years, just like summer in the Southern Hemisphere. Each calendar year includes parts of two winters. This causes ambiguity in associating a winter with a particular year, e.g. "Winter 2018". Solutions for this problem include naming both years, e.g. "Winter 18/19", or settling on the year the season starts in or on the year most of its days belong to, which is the later year for most definitions.