I was listening to Mac this morning and he said Sunday is the first day of the week. I don't recall hearing that before as Sunday is part of the weekend and Monday is the first day of the week. However:
https://www.timeanddate.com/calendar/days/monday.htmltimeanddate wrote:
Monday: the Moon’s Day
Monday is the first day of the week according to the international standard ISO 8601, but in the US, Canada, and Japan it's counted as the second day of the week.
Monday comes after Sunday and before Tuesday in our modern day Gregorian Calendar.
Naming Monday
The English word Monday is derived from Old English and means “the Moon’s day”.
Middle English – Mondayor mone(n)day
Latin – dies lunae – Day of the moon
Old Norse - mánadagr, mandag, mánudagur
Old English – mōnandægor mōndæg
Ancient Greek – hemera selenes – Day of the moon
First or Second Day?
Monday is considered the first day of the week according to the international standard ISO 8601. In many cultures and languages, Monday is given a name that means either “second day” marking Sunday to be the first day of the week or a name that means the day after Sunday.
Slavic languages number Monday as the first day, not the second day. Most European countries' calendars show Monday as the first day of the week.
Holidays on a Monday
Several US holidays always fall on a Monday such as Labor Day, Memorial Day, Columbus Day, and Veteran’s Day. In the UK, there are three bank holidays on Mondays plus Easter Monday, which is also a day off.
Long weekends in the US and UK
Depressing “Blue” Monday
Monday used to be called “Blue Monday” because it was a day associated with washing clothes that involved blue dye. However, it now refers to the day employees reluctantly return to work after the weekend.
Least Favorite Day
In many cultures, Monday is considered the worst day of the week because it is the first day of the work week. Song lyrics often feature Monday as a day of depression, anxiety, or melancholy such as “Monday, Monday” by the Mamas & the Papas in 1966 or “Rainy Days and Mondays” by the Carpenters in 1971, not to mention “I Don't Like Mondays” by the Boomtown Rats in 1979.
However, Mondays are considered good days for fasting in Judaism and Islam. In the Eastern Orthodox Church, Angels are commemorated on Mondays.