The seven-day week
The seven-day week is the international standard week (ISO 8601) used by the majority of the world. A year adds up to 52 weeks, but countries vary on exactly how they count and number the weeks.
The seven-day-week provides a clear method of representing dates and times to avoid misinterpretation between people from different countries with varying traditions for writing numeric dates and times.
Naming 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 r elationship between the week days and the planets.
52 or 53 weeks?
The weeks of the year in a Gregorian calendar are numbered for each year. These week numbers are commonly used in some European and Asian countries; but not 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.
Monday or Sunday 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 is 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.
When is the weekend?
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. Christians mark Sunday as their day of rest and worship, while Muslims refer to Friday as their day of rest and worship.
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).
There are many different opinions as to how 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 and Germanic and Norse people later did the same with some of their own 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.