Editing Roger Bacon (section)

====Calendrical reform====
{{hatnote|Main: [[Calendrical reform#Julian and Gregorian reforms|Calendrical reform]] and [[Gregorian calendar#Gregorian reform|Gregorian calendar]]}}
In Part IV of the ''{{lang|la|Opus Majus}}'', Bacon proposed a [[Calendar reform|calendrical reform]] similar to the later [[Gregorian calendar#Gregorian reform|system]] introduced in 1582 under [[Pope Gregory XIII]].<ref name=baconI4/> Drawing on [[Ancient Greek astronomy|ancient Greek]] and [[Astronomy in the medieval Islamic world|medieval Islamic]] astronomy recently introduced to western Europe via Spain, Bacon continued the work of [[Robert Grosseteste]] and criticised the then-current [[Julian calendar]] as "intolerable, horrible, and laughable".

It had become apparent that [[Eudoxus of Cnidus|Eudoxus]] and [[Sosigenes of Alexandria|Sosigenes]]'s assumption of a year of 365¼ days was, over the course of centuries, too inexact. Bacon charged that this meant the [[computus|computation of Easter]] had shifted forward by 9 days since the [[First Council of Nicaea]] in 325.<ref name=dunkin>{{citation |last=Duncan |first=David Ewing |author-mask=Duncan |title=The Calendar |date=2011 |pages=1–2 }}</ref> His proposal to drop one day every 125 years<ref name=baconI4>{{harvp|Bacon|1897|loc=[https://archive.org/details/opusmajusrogerb01bridgoog Vol.&nbsp;I], [https://archive.org/stream/opusmajusrogerb01bridgoog#page/n293/mode/2up Pt.&nbsp;IV] }}</ref>{{sfnp|North|1983|pp=75, 82–84}} and to cease the observance of fixed [[equinox]]es and [[solstice]]s<ref name=dunkin/> was not acted upon following the death of [[Pope Clement IV]] in 1268. The eventual [[Gregorian calendar]] drops one day from the first three centuries in each set of 400 years.