Questions about the Calendar

7 days a week, 52 weeks a year and 365 days a year (unless in a year not divisible by 400 where it is 366 days a year). Why is it that way and not another way? While we have talked about Leap Year in fact card #61, here we should talk about why our calendar is the way it is.
Why do we have 365 days in years divisible by 400?
The earth takes 365.35 days to orbit the Sun in one solar year but we usually round this to simply 365 days and this timeframe has 52 weeks. The Ancient Egyptians are said to have created one of the first 365 day calendar which seems to have begun in 4236BCE with a system similar to the Babylonians (who were in what we now call Iraq) as it had 12 months of the year.
Why do we have 7 days a week?
Other than 7 being the amount of days God is said to have created the universe and the world, the Babylonians of ancient days Iraq are the reason why we have a seven day week. They were absolute observers and observed 7 celestial bodies which included the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn. The Romans adopted the seven day week during the reign of Emperor Constantine 1 in 321CE where he designated Sunday as the first day of the week.
Why do we have 12 months?
Like Leap Year, the 12 month system was created by Julius Caesar and his astronomers. He and his team created a calendar with 12 months and 365 days with the 4th year having an added date to create 366 days. In the old calendar, there were 10 months and the year began on 1 March but the Julian calendar had 12 months and began on 1 January. As for the odd numbered months that weren't February, that's just how Julius wanted it
How did the days of the week get their name?
Monday: its name is related to the moon. In Latin, Luna means moon which is why in French Lundi is Monday. Tuesday: comes from the Old English Tiwesdaeg after Tiw who was a one handed Norse god of duelling.
Wednesday: the namesake for a raven haired gothic girl, the day Wednesday got its name from the god Woden (who is best known as Odin in Norse Mythology) from Germanic paganism.
Thursday: the Out of Touch and throwback day got its name from another god of pagan religions and he has been loved by hero film fanatics alike, Thor! Before he was utilised by comic books, Thor was the Norse god of thunder and Thursday came from Thor's Day or as it is in Old English: Pūnresdæg.
Friday: the best day of the week came from Frjádagr or Frigg AKA Freya, the wife of Odin who was also Thor's daddy.
Saturday: back to the Rome for this one as the day where comedy is broadcasted live from New York City came from the Roman god Saturn, the Roman god of time. In Latin, his day was called Dies Saturni.
Sunday: the Christian day of rest got its name from the Latin dies solas (sun's day) though it also has a Germanic interpretation called Sunnandæg.