The Days of the Week
The seven-day week is used by the majority of the world and has become the international standard as specified by the International Organization for Standardization (ISO 8601). It provides a clear method of representing dates and times to avoid misinterpretation of data transferred between countries with different conventions for writing numeric dates and times.
The History of the Seven-day Week
There are many different opinions as to how the history of the seven-day week came about, but the most common explanation is that the seven-day week seems to have originated when Babylonian astrologers assigned their planet gods to the days of the week around 700 BCE. The Romans later replaced these names with their own planet-gods.
Astrology has had a major influence on our weekly calendar in which it is responsible for the order of the days. Ancient Mesopotamian astrologers linked a planet-god to each hour of the day and then arranged them to their correct cosmological order. They used a seven-sided figure to keep track of the proper names of the hours and days in relation to the planet gods where each vertex was marked with a planet’s name in the proper order.
The Naming of the Days
Most Latin-based languages derived the names of the seven days of the week from the Roman period where they related each day of the week with the seven planets, the Sun, the Moon, Mercury, Venus, Mars, Jupiter, and Saturn.
The English language has retained these names for Saturday, Sunday, and Monday, however the planet names for the other days of the week (Tuesday, Wednesday, Thursday, and Friday) were replaced by their equivalent Norse gods. Some Asiatic languages such as Hindi, Japanese and Korean have a similar relationship between the week days and the planets.
The Week Number
The weeks of the year in a Gregorian calendar are numbered for each year. It is most commonly used in some European and Asian countries; it is not commonly used in the United States.
This numbering system for weeks begins on a Monday and is associated with the year that contains that week’s Thursday, thus if a year starts in a long weekend (Friday - Sunday) week number one for that year will start after that.
Most years have 52 weeks but if the year starts on a Thursday or is a leap year that starts on a Wednesday, that year will have 53 weeks. It is important to note that there are at least six different numbering systems for weeks that are currently in use around the world.
The First Day of the Week
The first day of the week varies all over the world. In most cultures, Sunday is regarded as the first day of the week although many observe Monday as the first day of the week. According to the Bible, the Sabbath or Saturday is the last day of the week which marks Sunday as the first day of the week for many Jewish and Christian faiths, while many countries regard Monday as the first day of the week.
According to the international standard ISO 8601, Monday shall be the first day of the week ending with Sunday as the seventh day of the week. Although this is the international standard, countries such as the United States still have their calendars refer to Sunday as the start of the seven-day week.
Which Day is the Day of Rest?
The day of rest can vary for each culture and religion. According to the Jews, the Sabbath or Saturday is the day of rest and worship because it was on this day that God rested after creating the world. Most Christians mark Sunday as their day of rest and worship because Jesus rose from the dead on a Sunday. Muslims refer to Friday as their day of rest and worship because the Quran calls Friday a holy day or the “king of days”.
Nowadays, both Saturday and Sunday are seen as days of rest, and some calendars show Monday as the first day of the week since it is the first day of the "work week" (Monday - Friday only).