How did humans set the first reference point for days of the week?

[william7580]

Last Tuesday ,I came across an old lady[looking a bit disorientated] in the street who asked me "Is today a Sunday ,I need to go to church?"
I said to her "Its a Tuesday" This set me thinking about "phases of the moon","364.25 days for Earth to orbit Sun", 52 weeks made up of 7 days etc etc. and to the question about a reference point in time ,before starting the calendar , when humans decided "We will call today a Saturday[ worship on the Sabbath] ,next day Sunday[worship of the Sun god]"

 

[robotpie3000]

I think the names given to the days of the week are just assigned by us humans and really has no physical significance, but I could be wrong.

 

[Bandersnatch]

Sunday used to be the first day of each of the four quarters of the lunar month in rarely used ancient Greek tradition, who otherwise used to divide months into three decades, which is more accurate.
The seven days were named after the seven celestial bodies known at the time, starting with the Sun and ending with Cronus. The division and naming scheme was adopted by Romans at some time in history, with names of the Greek gods used for planets changed to their Roman equivalents. Saturday is then Saturn's day(Roman Saturn=Greek Cronus), and the last day of the week.
One of the reasons for entrenchment of the seven day week division is the influence of Jewish numerological tradition via Christianity.
In the English language, four of the days of the week got their names changed to those of Germanic pantheon.

In the ancient Romulan (as in Romulus', not from Star Trek, mind you) calendar the time of the year was counted from the first lunar phase after winter cold abated enough to allow working the fields.

Thus we could say that Sunday is the first day after the first new Moon in Spring, and every seventh day thereafter - but such explanation would be anachronistic. By the time of the seven day week adoption, the Roman calendar was already divorced from lunar observations and agrarian tradition, and which particular diurnal cycles of the year ended up as particularly named days is best though of as a product of chance and arbitrary decisions of calendar codifiers.