7 days in a week and 4 weeks in a month. That bothers me a lot. I really wonder why there are seven days in a week, and why there are 4-5 weeks in a month? But there is no 7‑day week in nature like 12 months in a year; so why a week, there are 7 days?

According to Mr.Peter Mayer- « People use a 7‑day week because they have been born into a world where this is customary. In other words, the 7‑day week has been received from earlier generations. It has a long history. When the Roman emperor Constantine made Christianity the state religion early in the 4th Century CE the 7‑day week was officially associated with the Julian Calendar, and the association remained after the Julian Calendar was replaced by the Gregorian Calendar in the 16th Century CE.The Christians received the 7‑day week from the Jews (in fact, the original Christians were Jews). The Jewish explanation for its use is that this was commanded by their god, named by them YHWH (using the Hebrew letters Yod-He-Vav-He). The Jewish Pentateuch (incorporated into the Old Testament of the Christian Bible) contains several injunctions attributed to YHWH which mention « a seventh day », upon which no « work » is to be done.Whether or not a 7‑day week was in use by the Jews at the time of Moses in the middle of the 2nd millennium BCE is highly debatable, since YHWH’s commands to Moses are not preserved in any contemporary records but only in documents which were composed around the middle of the first millennium BCE.« .

Well, his answer does not satisfy me very much since the 7‑day week is older than the Hebrews. And why so? For my private opinion, I think it’s because long long time ago, the old astronauts could possibly find 7 planets. Then they named them and used them as a week. This idea links to a point that in many European languages, names of the days of the week are derived from those 7 planets.

« Many reasons are given for the seven-day week — probably it’s the result of several of the following factors taken together: the four phases of the moon are roughly seven days in length; the Babylonians believed in the sacredness of the number seven; in ancient times, seven planets (including the sun and moon) were thought to exist (and indeed the days of the week were named after them). The Mosaic sabbath defined a seven-day period, and the dispersed Jews who observed it may have influenced the establishment of the seven-day week — it first appears in the early Christian era. » Mr.Brendon Bangma, an Australian student from a uni in Holland.

Hmm, his answers seem to conect my points I’ve said above that the old astronauts could only find 7 planets. What about the moon phases? I thought the moon has 8 phases such as New Moon, New Crescent, First Quarter, New Gibbous, Full Moon, Old Gibbous, Last Quarter, and Old Crescent. But it’s possibly correct that First Quarter and  Last Quarter, New Moon and full Moon, New Gibbous and Old Gibbous, New Crescent and Old Crescent look the same.