How Many Weeks Are in a Year?

By Staff WriterLast Updated May 27, 2020 7:17:52 PM ET
Weeks
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Most years in the Gregorian calendar have 52 full weeks and one day. Leap years have 52 full weeks and two extra days. Certain years in the Gregorian calendar, however, will have 53 numbered weeks. These are the years when January 1 falls on a Thursday or is a leap year that starts on a Wednesday. While such numbered years are commonly used in Asian and European countries, they are not as popular in the US.

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The 7-Day Week

Of all the units of time in a year, only the seven-day week is an artificial period of time. The day is based on the 24-hour night-day cycle, the month on the cycle of the moon phases, and the year on the time it takes Earth to complete an orbit around the Sun. The week is unique in that it is not based on any astronomical phenomenon that constitutes a unit of time.

It is generally accepted that the seven-day week was adopted from the biblical account of the creation where it took God six days to create the universe and then rested on the seventh day. This is reflected in the seven-day period for the ancient Israelites where they work for six days and dedicate the seventh day to rest and for worshipping God. Some theorize that the Israelites may have adopted the seven-day week from earlier religious traditions of the Sumerians and Babylonians.

Days of the Week

Many historians are in agreement that it was the Romans who firmly established the modern seven-day week, by adding features from the Babylonians’ seven-day week system. This is evidenced by some of the days of the week being named after Roman deities. These days are Sunday, which the Romans dedicated to the Sun god, Monday for the Moon god, and Saturday for Saturn. The Romans used to have eight days a week as a civil practice until 321 C.E. when Emperor Constantine established the seven-day week.

Anglo-Saxon Influence

Other Roman deities inspired the name of the other days of the week such as Mars’ day (Tuesday), Mercury’s day (Wednesday), Jupiter’s day (Thursday) and Venus’ day (Friday). The days of the week in other languages, particularly those belonging to the Romance language still bear this influence.

The names in English of days of the week, however, apart from Saturday, Sunday and Monday, have Anglo-Saxon origins. Names of the gods of Teutonic Mythology were used for the other weekdays. Tuesday was derived from Tiu, which is the Anglo-Saxon name for the Norse god of war Tyr. Wednesday was named after Woden, the Anglo-Saxon name for the Norse supreme god Odin, while Thursday was named after the god of thunder, Thor. Friday or Frigg’s day was named after Frigg, the wife of Odin.

Does the Week Start on a Sunday or Monday?

When Emperor Constantine established the seven-day week in 321 C.E., he also designated Sunday as the start of each week. Calendars and week numbering systems in the United States, Canada, Australia, and New Zealand also start each week on a Sunday.

The International Standard ISO 8601, which is the most common week numbering system in the world, starts the week on Monday and ends on Sunday. Using the ISO 8601 will help mitigate the confusion and doubt in international correspondence between different week numbering systems and time zones.

Weekdays and Weekends

Most of Christendom dedicate Sunday as a day for worship or rest. Islam, on the other hand, designates Friday as their day of rest. Judaism has long designated Saturday as the day of Sabbath and rest. Traditional calendars mark weekend days as red to make them stand out from the rest of the weekdays, which are usually colored blue or gray.