A week consists of 7 days, and each day 24 hours.
Each two hours are dedicated consecutively to one of the celestial bodies according to the following order:
Saturn土, Jupiter木, Mars火, Sol日, Venus金, Mercurius水, Luna月.
If the day starts with Saturn, the 25th and 26th hours (the next day) will be dedicated to Sol.
If the day starts with Sol, the 25th and 26th hours (the next day) will be dedicated to Luna and so on.
The names of the days in a week are therefore established in such order:
Dies Solis日. Sunday. Sun's day.
Dies Lunae月. Monday. Moon's day. (Lunedi, Lundi in Italian and French)
Dies Martis火. Tuesday. Tiws day. (Martedi, Mardi in Italian and French)
Dies Mercurii水. Wednesday. Wodens day. (Mercoledi, Mercredi in Italian and French)
Dies Jovis木. Thursday. Thors day. (Giovedi, Jeudi in Italian and French)
Dies Veneris金. Friday. Friggs day. (Venerdi, Vendredi in Italian and French)
Dies Saturni土. Saturday. Saturn's day.
DAYS IN THE MONTHS OF THE YEAR
By the order of Julius Caesar all odd months have 31 days and even months 30 days except February which has 28 or 29 days.
(Julius Caesar, the last Roman dictator,100 - 44 B.C.)
Later, following the example of Julius who renamed Quintilis (the fifth month) into July, Augustus renamed Sextilis (the sixth month) into August as well as making it 31 days, although it is an even month.
(Augustus, the first Roman Emperor, 63 B.C. - 14 C.E.)
And to avoid having three months with 31 days consecutively, he changed all odd months after August into 30 days and all even months into 31 days.