https://calendartruth.info/october-4th-1582-october-4th-2016-434-years-of-an-irrational-and-artificial-time-system/?dcode_day=10&dcode_mo=5&dcode_yr=2020
Reasons that a 13, 28 day cycle (moon rotates around earth in 28 days 12x, and earth rotates around sun 1x = 12+1) is natural and Gregorian calendar is a manipulation of time.