Astronomy defines most of the major units of time used in daily life: a year is the time Earth takes to orbit the sun once; a month is the time the moon takes to orbit the Earth once; a day is the time the Earth takes to rotate on its axis once. But what about the week? It is not a naturally occurring phenomenon, but rather a human invention (though in Latin-based languages it usually relates to astronomy.) Why seven days, and how were the names derived?
Naming the Days Based on Order
The seven-day week goes back to ancient times. There are several theories about the origin of the seven-day week, and it is possible that it was arrived at independently by different cultures and for different reasons. Numerous names are therefore used today by different cultures.
Some naming systems are simply based on order. Russian, for instance, uses the following: Monday = Ponedelnik (“do-nothing”), Tuesday = Vtornik (second), Wednesday = Sreda (middle), Thursday = Chetverg (fourth), Friday = Pyatnotsa (fifth), Saturday = Subbota (sabbath), and Sunday = Voskresenye (resurrection).
Naming the Days After Major Celestial Bodies
The familiar English week names are not linked to order, but instead to the seven major celestial bodies known to the ancients. The sun and moon were especially obvious, but five other bodies also highlighted the night skies. These five became known as the planets, from the Greek word planetes, meaning the wanderers, and were named by the ancient Babylonians for their important gods and goddesses.
In addition to English, most other Latin-based languages use the Roman versions of these mythological characters to identify the planets. One wonders how the days of the week would be named today, since nine major celestial bodies (the sun, moon, and seven official planets), are now recognized based on the current definition by astronomy’s governing body, the International Astronomical Union.
English and Spanish Weekday Names
Sunday is named after the sun and comes from the Latin dies solis, meaning the day of the sun. In Spanish, Sunday is known as Domingo. Monday is named in honor of the moon and comes from the Latin dies lunae, the day of the moon. The Spanish word for Monday, Lunes, directly derives from the Latin term, as is the case for most of the Spanish planet names.
Tuesday is named after Tiw, the Anglo-Saxon god of war, whose Roman equivalent was Mars. Mars, in turn, is from the Latin Martis, which also leads to the Spanish Martes. Wednesday derives from the chief Norse god Woden, which is identified with the Roman god Mercury. This name is from the Latin Mercuii (Spanish is Meircoles.) The fifth day of the week, Thursday, is after the Norse god Thor, associated with the Roman king of gods Jupiter. Jupiter is from the Latin Jove (Spanish is Jueves).
Friday is from the Nordic goddess Freya, similar to the Roman goddess of love Venus (Latin is Veneris, Spanish is Viernes). Finally comes one of our favorite days, Saturday, from the Roman god of agriculture Saturn (Latin is Saturni, Spanish is Sabado).
Astronomy in Everyday Life
Like many major units of time, the week has astronomical ties. For most Latin-based languages the week is broken down into seven parts based on the seven ancient celestial bodies, and each of these bodies lends its name to one of the units, or days. This is an excellent example of the importance of astronomy to ancient cultures and its impact today.