What happened on October 15?

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  The Missing 10 Days of 1582 Urban Legends

  If you display October 1582 in a smartphone calendar, the 4th is followed by the 15th, with ten days missing. The cause is the calendar reform (the Gregorian calendar) by Pope Gregory XIII, which really did skip ten days.

Events based on the old lunar calendar, or festivals whose dates vary by year, are shown on approximate dates.