I am wondering about the history about the beginning of the week. Although some recent calendars start their week on Monday, "traditionally", the Japanese start their week on Sunday (so that 今週の日曜日 will always be in the past). But this is a fairly new tradition.
Why was Sunday made the beginning of the week when Japan adopted the Gregorian calendar?
There is a lunar calendar (睦月, 如月, 弥生, etc.) and a solar calendar (七十二候). Furthermore, there is the concept of auspicious days, in which a week has 6 days and a bunch more of calendar-type conventions.
Do any of these contain a "Sunday" as beginning of their respective concepts of a week?