Português: Rosto da Bula papal "Inter Gravissimas" de Gregório XIII estabelecendo a Reforma do Calendário Gregoriano.
English: The first page of the papal bull "Inter Gravissimas" by which Pope Gregory XIII introduced his calendar.
Seasonal error of Gregorian calendar
English:An Election Entertainment - includes famous "Give us our Eleven Days" protest slogan against the Gregorian calendar at lower right (on black banner on floor under foot).
Deutsch: 400 Jahre Gregorianischer Kalender)
English: Stamp, four hundred years of the Gregorian Calendar
English: Comparing two different definitions of the tropical year (from spring equinox to spring equinox, and time needed by the mean sun for 360° on the ecliptic) with the length of the Gregorian calendar year, allowing for the slowing-down of the Earth's rotation.
English: The date of the northern summer solstice between 1750 and 2250
Look up day of week for any Gregorian date
Deutsch: Ewiger Gregorianischer Kalender ab dem 15. Oktober 1582
In September 1752, Britain changed from Old Style (O.S.) to New Style (N.S.)
This is what common calendars look like today, often with an image or picture representing the month.