Origins of the Days of the Week

Yes, there is a connection between the days of the week and the Solar system, but it's not quite as direct and a bit more complicated than you assume in your question. First of all, we may know of nine planets today, but the ancients were unaware of the three outer planets Uranus, Neptune, and Pluto since they can only be seen by telescope. When the ancients did gaze into the sky, however, they noted seven objects that were clearly different than the fixed points of light that we now know to be stars. The most obvious of these different objects were the Sun and the Moon. The other five were points of light that looked like stars but moved across the night sky in a much different manner than stars. These five objects that appeared to wander across the sky are what we now know to be the five planets closest to Earth--Mercury, Venus, Mars, Jupiter, and Saturn. It is these seven celestial objects for which the days of the week were originally named. Or to be more precise, the days of the week were named in honor of the same gods for which the planets are named.

Ptolemaic concept of the universe
Ptolemaic concept of the universe

Some of the connections are quite obvious in the English language. For example, Sunday is named for the Day of the Sun, Monday is the Day of the Moon, and Saturday is short for the Day of Saturn. The remaining names are a bit less obvious in English, but if we look at their Latin names, the connections become more clear.

The names of the planets we still use today are based on names given by the ancient Greeks, who named the planets for their greatest gods. Since the Latin-speaking Romans utilized the same pantheon of gods, they merely substituted the names of their gods in place of the Greek mythology. The romance languages of southern Europe (French, Italian, Spanish), still call the days of the week by names based on these Latin origins. The Germanic peoples of northern Europe also employed the same traditions in naming the days of the week, but instead substituted many of their own roughly equivalent gods in place of the Roman names. Let's take a closer look at each day.


The original name for the first day of the week comes from the Greek hemera heliou, or "day of the sun" named in honor of the Greek sun god Helios. The Romans substituted their own sun god, Sol, and named the day dies solis, meaning "sun's day," in Latin. Once Christianity had taken hold in Rome and sun worship had lost favor, the day became known as dies Dominica, Latin for the "day of God." However, the "day of the sun" continued to be honored in northern Europe, as exemplified by the Germanic sunnon-dagaz and Anglo-Saxon sunnandæg. The name evolved in Middle English as sonenday to soneday to sunnenday and finally to Sunday.

Day of the Sun
Greek: hemera heliou Latin: dies solis Anglo-Saxon: sunnandæg
French: dimanche Italian: domenica Spanish: domingo
English: Sunday German: Sonntag Dutch: zondag
Danish: søndag Norwegian: søndag Swedish: söndag


The second day of the week was sacred to the goddess of the Moon, called Selene in Greek, and named hemera selenes for "day of the moon." The Romans named the day dies lunae in honor of their moon goddess Luna. The English word can be traced to the Anglo-Saxon monandæg, or "moon's day," which evolved to mondæg, monenday, moneday, and eventually to Monday.

Day of the Moon
Greek: hemera selenes Latin: dies lunae Anglo-Saxon: monandæg
French: lundi Italian: lunedi Spanish: lunes
English: Monday German: Montag Dutch: maandag
Danish: mandag Norwegian: mandag Swedish: måndag


This day was first named for the Greek god of war Ares, or hemera Areos, and later for the Roman god of war Mars, dies Martis. Mars was associated with the fourth planet because of its reddish hue. The English name comes from the Anglo-Saxon tiwesdæg, or "Tiw's day." Tiw (or Tiu, Twia) was the Germanic god of war and the sky based on the Norse god of war Tyr (or Tir). The word changed over time from tiwesday to tewesday to Tuesday.

Day of Mars
Greek: hemera Areos Latin: dies Martis Anglo-Saxon: tiwesdæg
French: mardi Italian: martedi Spanish: martes
English: Tuesday German: Dienstag Dutch: dinsdag
Danish: tirsdag Norwegian: tirsdag Swedish: tisdag


The planet that moves most quickly across the night sky is that closest to the sun, so the ancient Greeks named it in honor of the swift messenger god Hermes. The "day of Hermes," or hemera Hermu, was also dedicated to him. The Latin name for this day was dies Mercurii, named for the Roman messenger god Mercury. The Anglo-Saxons named the day wodnesdæg for Woden, the god of the wild hunt. Woden was based on the Norse god Odin. "Woden's day" evolved to wodnesday, wednesdai, and the modern English word Wednesday.

Day of Mercury
Greek: hemera Hermu Latin: dies Mercurii Anglo-Saxon: wodnesdæg
French: mercredi Italian: mercoledi Spanish: miércoles
English: Wednesday German: Mittwoch Dutch: woensdag
Danish: onsdag Norwegian: onsdag Swedish: onsdag


The Greek hemera Dios, or "day of Zeus," was named for the supreme god of the heavens Zeus. The Romans likewise named the day dies Jovis, or "Jove's day," in honor of Jove, which is another name for Jupiter. Jupiter, the fifth planet, was the chief god of Roman religion who hurled lightning bolts from Mount Olympus. Jupiter's counterpart in Norse mythology was Thor, the god of strength and thunder. The Old Norse thorsdagr, or "Thor's day," was named in his honor. The Anglo-Saxon equivalent was thursdæg or thunresdæg, for "thunder's day." The Middle English thuresday evolved into Thursday.

Day of Jupiter
Greek: hemera Dios Latin: dies Jovis Anglo-Saxon: thursdæg
French: jeudi Italian: giovedi Spanish: jueves
English: Thursday German: Donnerstag Dutch: donderdag
Danish: torsdag Norwegian: torsdag Swedish: torsdag


Both this day and the second planet were dedicated to the goddess of love--the Greek Aphrodite, hemera Aphrodites, and Roman Venus, dies Veneris. The English word is derived from the Germanic frije-dagaz for "Frigg's day" or "Freya's day." Frigg and Freya (Fria) were both goddesses of Germanic and Norse mythology associated with love, beauty, and procreation. The modern word Friday is based on the Middle English fridai.

Day of Venus
Greek: hemera Aphrodites Latin: dies Veneris Anglo-Saxon: frigedæg
French: vendredi Italian: venerdi Spanish: viernes
English: Friday German: Freitag Dutch: vrijdag
Danish: fredag Norwegian: fredag Swedish: fredag


The final day of the week was called hemera Khronu by the Greeks in honor of the god Cronus (or Kronos) who ruled the universe until dethroned by his son Zeus. The Romans named the day dies Saturni for the god Saturn, counterpart to Cronus and also the god of agriculture, who was associated with the sixth planet. The Anglo-Saxon sæternesdæg and sæterdæg, or "Saturn's day," evolved to saterday and is the root of the English word.

Day of Saturn
Greek: hemera Khronu Latin: dies Saturni Anglo-Saxon: sæterdæg
French: samedi Italian: sabato Spanish: sábádo
English: Saturday German: Samstag Dutch: zaterdag
Danish: lørdag Norwegian: lørdag Swedish: lördag

In summary, most historians agree that our week is made up of seven days because of the seven primary celestial objects observed by ancient astronomers--the Sun, Moon, and five planets observable with the naked eye. In most European languages, particularly those more closely based on Latin, these days are named for the same ancient gods as those seven bodies of the Solar system.
- answer by Joe Yoon, 15 June 2003

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