Editing Leap year (section)

==Islamic calendars==
The observed and calculated versions of the lunar [[Islamic calendar]] do not have regular leap days, even though both have lunar months containing 29 or 30&nbsp;days, generally in alternating order. However, the [[tabular Islamic calendar]] used by Islamic astronomers during the Middle Ages and still used by some Muslims does have a regular leap day added to the last month of the lunar year in 11&nbsp;years of a 30-year cycle.<ref name=timeanddateIslamicCalendar>{{citation | url = http://www.timeanddate.com/date/islam-leap-year.html | title = The Islamic leap year | date = n.d. | publisher = Time and Date AS | access-date = 29 February 2012 | archive-date = 3 March 2020 | archive-url = https://web.archive.org/web/20200303004338/http://www.timeanddate.com/date/islam-leap-year.html | url-status = live }}</ref> This additional day is found at the end of the last month, [[Dhu al-Hijjah]], which is also the month of the [[Hajj]].<ref name=GMANewsLeapYearTrivia>{{citation | url = http://www.gmanetwork.com/news/story/249829/lifestyle/people/leap-year-trivia-you-might-want-to-know | title = Leap year trivia you might want to know | date = n.d. | publisher = GMA News | access-date = 29 February 2012 | archive-date = 15 May 2013 | archive-url = https://web.archive.org/web/20130515233835/http://www.gmanetwork.com/news/story/249829/lifestyle/people/leap-year-trivia-you-might-want-to-know | url-status = live }}</ref>

[[Image:Jalaali_Leap_Year.svg]]
{{see also||Jalali calendar }}
The [[Solar Hijri calendar]] is the [[Iranian calendar#Modern calendar (Solar Hejri)|modern Iranian calendar]]. It is an observational calendar that starts on the [[spring equinox (Northern Hemisphere)]] and adds a single intercalated day to the last month (Esfand) once every four or five&nbsp;years; the first leap year occurs as the fifth year of the typical 33-year cycle and the remaining leap years occur every four&nbsp;years through the remainder of the 33-year cycle. This system has less periodic deviation or jitter from its mean year than the Gregorian calendar and operates on the simple rule that New Year's Day must fall in the 24&nbsp;hours of the vernal equinox.<ref name=jitter>{{citation |last=Bromberg |first=Irv |title=Fixed Arithmetic Calendar Cycle Jitter |publisher=University of Toronto |url=http://individual.utoronto.ca/intervalmath/ |access-date=24 October 2019 |archive-date=24 October 2019 |archive-url=https://web.archive.org/web/20191024025932/http://individual.utoronto.ca/intervalmath/ |url-status=live }}</ref> The 33-year period is not completely regular; every so often the 33-year cycle will be broken by a cycle of 29&nbsp;years.<ref>{{citation | first = M. | last = Heydari-Malayeri | url = http://aramis.obspm.fr/~heydari/divers/ir-cal-eng.html | title = A Concise Review of the Iranian Calendar | publisher = Paris Observatory | date = 2004 | arxiv = astro-ph/0409620 | bibcode = 2004astro.ph..9620H | access-date = 19 December 2010 | archive-date = 16 July 2011 | archive-url = https://web.archive.org/web/20110716115426/http://aramis.obspm.fr/~heydari/divers/ir-cal-eng.html | url-status = live }}</ref>

The Hijri-Shamsi calendar, also adopted by the [[Ahmadiyya]] Community, is based on solar calculations and is similar to the Gregorian calendar in its structure with the exception that its [[epoch]] is the [[Hijra (Islam)|Hijra]].<ref>{{citation | url=http://www.alislam.org/library/history/ahmadiyya/73.html | title=Hijri-Shamsi Calendar | publisher=Al Islam | date=2015 | access-date=18 April 2015 | quote=The time frame in these months is the same as [...] the months of a Christian calendar. | archive-date=26 January 2017 | archive-url=https://web.archive.org/web/20170126203234/https://www.alislam.org/library/history/ahmadiyya/73.html | url-status=live }}</ref>