What is the first day of the week?

The first day of the week is Monday. A week is a time unit equal to seven days and it is the standard period used worldwide. In English, the names for a week are Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, and Sunday, then returning to Monday. The seven-day cycle runs independently of the cycle of a (year) calendar.

   The ISO 8601 standard (International Organization for Standardization), which helps remove doubts that can result from the various day and date conventions, cultures, and time zones that impact a global operation, sets a clearly defined and understandable date and time format to both people and machines. At this point it is interesting to mention that the name of ISO origins from the Greek isos (ίσο), meaning equal.

   Hence, ISO 8601 sets out an internationally agreed way to represent dates as YYYY-MM-DD. For instance, January 10, 2023, is represented as 2023-01-10. ISO 8601 was established in 1988 and it can be used by anyone who wants to use a standardized way of presenting date and time. But why it is so important to make standards about time and date formats?

   To answer this, we must think about our daily obligations. If the first day of the week was different depending on politics or management, then how we could set up job tasks properly? How could we schedule flights and public transport? What about keeping public records? How could it be possible to manage deadlines and projects, or schedule meetings and business or leisure events? Therefore, we need a general standard, setting that Monday is the first day of the week worldwide.

   The days of the week are named after classical planets or gods of a pantheon in some countries, while generally a week may be called a planetary week. The Hebrew Bible offers the explanation that God created the world in six days, while in the seventh day, God rested from his work of creating the world. Shabbat (equivalent to Saturday) became the day of worship and rest in Jewish tradition and the last day of the week, while the following day, Sunday, is the first one in the Hebrew week.

 

A week in Greek: Δευτέρα, Τρίτη, Τετάρτη, Πέμπτη, Παρασκευή, Σάββατο, Κυριακή

A week in English: Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday

A week in planets (Greek): Σελήνη, Άρης, Ερμής, Δίας, Αφροδίτη, Κρόνος, Ήλιος

A week in planets (English): Moon, Mars, Mercury, Jupiter, Venus, Saturn, Sun

 

   In the Gregorian calendar, which is used in most of the world (introduced in October 1582, by Pope Gregory XIII as a modification of, and replacement for, the Julian calendar), one week has seven days, while a full calendar year has 52 weeks + 1 day (2 days in a leap year). Indo-Europeans do not seem to have had an intermediate unit of time between the month and the day, which explains why hebdomas (εβδομάδα) from Hellenistic/Christian era became very important term, with the significance of the seven days. In Greek, the week is called εβδομάδα, which means a seven-day period.