Editing New moon (section)

===Hebrew calendar===
The new moon, in Hebrew [[Rosh Chodesh]], signifies the start of every Hebrew month and is considered an important date and minor holiday in the [[Hebrew calendar]]. The modern form of the calendar practiced in Judaism is a rule-based [[lunisolar calendar]], akin to the [[Chinese calendar]], measuring months defined in lunar cycles as well as years measured in solar cycles, and distinct from the purely lunar [[Islamic calendar]] and the predominantly solar [[Gregorian calendar]]. The Jewish months are fixed to the annual seasons by setting the new moon of [[Aviv]], the ''barley ripening'', or ''spring'', as the first moon and head of the year.<ref>{{Bibleverse|Exodus|12:1-2|HE}}</ref>  Since the [[Babylonian captivity]], this month is called [[Nisan]], and it is calculated based on mathematical rules designed to ensure that festivals are observed in their traditional season. Passover always falls in the springtime.<ref>{{Cite web |last=Posner |first=Menachem |year=2016 |title=How Does the Spring Equinox Relate to the Timing of Passover? |url=http://www.chabad.org/holidays/passover/pesach_cdo/aid/495531/jewish/How-Does-the-Spring-Equinox-Relate-to-the-Timing-of-Passover.htm |access-date=9 December 2016 |website=Chabad}}</ref> This fixed lunisolar calendar follows rules introduced by [[Hillel II]] and refined until the ninth century.  This calculation makes use of a mean lunation length used by [[Ptolemy]] and [[Lunar theory#Babylon|handed down from Babylonians]], which is still very accurate: ca. 29.530594 days vs. a present value (see [[#Determining new moons: an approximate formula|below]]) of 29.530589 days.  This difference of only 0.000005, or five millionths of a day, adds up to about only four hours since Babylonian times.{{citation needed|date=May 2015}}