calendar: Quick Facts

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Photos and Videos

Kalendarium (“Calendar”) by Regiomontanus

Infographic showing date formats: Day-Month-Year (most of world), Year-Month-Day (China, Japan, etc.), and Month-Day-Year (United States).

Illuminated manuscript page by the Limbourg brothers showing a procession of nobles on horseback in elaborate medieval dress, with a blue astrological calendar arch above.

Aerial view of Stonehenge stone circle with large upright and fallen stones arranged on green grass.

Circular diagram of the Jewish religious year showing Hebrew months around the outer ring and Gregorian months inside, with major holidays and fasts such as Rosh Hashanah, Yom Kippur, Sukkot, Hanukkah, Passover, and Purim labeled with their dates.

Late 18th-century Tibetan manuscript showing colorful illustrations of the twelve Chinese zodiac animals, each surrounded by handwritten script and calendar markings.

Circular illustration of the Chinese zodiac with animal symbols, including dragon, snake, horse, and tiger, arranged around a central yin-yang symbol on a purple patterned background.

Aztec calendar stone

Felipe Guamán Poma de Ayala: El primer nueva corónica y buen gobierno, depiction of an Inca bookkeeper using a quipu

Kiowa calendar painting

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Topics

world calendar International Fixed Calendar lunisolar calendar Inca calendar date sacred calendar Gregorian calendar Our Days Are Numbered: 7 Crazy Facts About Calendars Advent calendar French republican calendar clock sundial Hourglass clepsydra chronometer chronograph gnomon 22 Questions About Time and Timekeeping Answered Daylight Saving Time dynamical time

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Key People

How did Ptolemy explain retrograde motion?

Ptolemy

Egyptian astronomer, mathematician, and geographer

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Dionysius Exiguus

canonist