1. Which Planet Does the "Fire" in Tuesday Stand For?
The seven characters used for the days of the week in Japan—Sun, Moon, Fire, Water, Wood, Metal, and Earth—represent the Sun, the Moon, and five planets. Tuesday corresponds to the day of Mars. [2] [1] In ancient Greek, it was called hemera Areos (Day of Ares), and in Latin, dies Martis (Day of Mars). Both refer to the planet Mars. [1]
The days of the week reached Japan from Tang Dynasty China. It is said that Kukai brought them along with the Sukuyokyo, an esoteric Buddhist scripture, arriving in the early Heian period. [3] The Sukuyokyo states that the seven luminaries are the Sun, the Moon, and five stars. These five stars were named after the Five Elements theory: Wood, Fire, Earth, Metal, and Water. These names became the translations for the days of the week. [1] [3] In the correspondence table of the Sukuyokyo, the celestial body for Tuesday is listed as Keikoku (Mars). [1]
Therefore, the "Fire" in the Japanese word for Tuesday is a name for Mars borrowed from the "Fire" element of the Five Elements theory. But why was "Fire" assigned to Mars? To understand this, we must first look at Mars itself.
2. Why Does Mars Look Red in the Night Sky?
Mars is a planet that orbits outside Earth. In the night sky, it appears to shine with a reddish hue. [5] NASA explains that the reason it looks red is that the iron contained in Martian rocks is rusted (oxidized). The red dust created by this rust covers the surface and swirls in the atmosphere. [4]
Ancient Romans associated the redness of Mars with blood, which is why they named it after their god Mars, according to NASA. [4] The same red color led to a connection with the god's name in Rome. However, within the scope of this research, there are no direct sources stating that the "Fire" element in China is derived from this redness. While the common point of redness is visible, we do not definitively claim that the "Fire" in Japan and China comes from its color.
3. What Did Ancient China Call Mars?
The old Chinese name for Mars is Keikoku. It is a name based on the Five Elements theory. [6] The reading is keikoku, not keiwaku, and the character for Kei is easily confused with the character for "firefly."
Because Earth orbits inside Mars, Earth overtakes Mars approximately every 780 days (about 2 years and 2 months). At that time, Mars appears particularly bright. In January 2025, its brightness was magnitude -1.4. [5] This close approach does not happen every year, but roughly every 2 years and 2 months.
Dictionaries explain that the name Keikoku was given because the star's brightness changes significantly and it exhibits retrograde motion (appearing to move backward through the star field). Large approaches were thought to be omens of disaster. [6] In Japan during the Edo period, it was sometimes read as natsuhiboshi (Summer Sun Star). [6]
This completes the eastern path leading to Japan. So, what happened to the day named after Mars as it traveled to Europe?
4. How Is the English Word Tuesday Linked to the God Tiw?
The English word "Tuesday" derives from the Old English Tiwesdæg (Day of Tiw). Tiw was a Germanic god who was considered the same as the Roman god Mars. Therefore, Tiw's Day is a direct translation of the Latin dies Martis. [7]
The National Astronomical Observatory of Japan explains that in Germanic languages, the Roman god Mars was replaced by the Germanic god Tiu/Ziu, resulting in words like Tuesday and Dienstag. The names for days in English and German are cited as examples where the names have moved away from the names of celestial bodies. [1]
Tiw is considered the same god as Týr in Norse mythology. Germanic names for Tuesday, including English, are named after Týr rather than Mars. [8] However, scholars have differing views on the role of Týr.
It is important to note that the meaning of the date did not change. Only the name for the "day of Mars" was replaced with a god's name. [1]
5. Could the German Word Dienstag Come from the Name of an Assembly?
The German word for Tuesday is Dienstag, and the Dutch word is dinsdag. Etymology dictionaries suggest that the first part of these words may derive from the Germanic assembly (ding or *þing*), which was a place where people gathered to discuss matters. [9]
A clue for this theory involves Roman inscriptions. The name "Mars Thincsus," recorded on Roman-side inscriptions, is cited as the clue. Tiw is strongly associated with assemblies, and this name can be read as meaning "Mars of the Assembly." [8] [9]
However, etymology dictionaries note that the origin of Dienstag is not certain. [9] Therefore, we cannot definitively say "Tuesday was the day of the assembly." Tuesday is a word that translated "Day of Mars." For Dienstag, the etymology is not determined, and theories differ. [9]
So far, all the Tuesdays we have looked at were named after Mars or a god claiming that day. Are there Tuesdays named after neither stars nor gods?
6. Why Do Some Slavic Languages Call Tuesday "Second"?
In some Slavic languages, Tuesday traces back to an Old Church Slavonic word meaning "second." The Russian word vtornik is an example. It is a name based on order, not on the names of stars or gods. [7]
We can categorize the names of Tuesday by how they were named. Japanese borrows the "Fire" name from the Five Elements to point to Mars. Latin uses the name of Mars, who is also a god. English uses the name of the god Tiw. German may contain the name of an assembly associated with Tiw, though this is only a possibility. Russian uses the order "second." Four naming methods—star, god, assembly, and order—have become the name for the same day.
7. How Can You Find Mars in the Night Sky?
The cycle in which Earth overtakes Mars is about 2 years and 2 months, and Mars appears particularly bright at those times. [5] The National Astronomical Observatory of Japan has a page called "Starry Sky Information" that announces when Mars will be bright. The cycle is only a rough guide, so check the exact dates there [5].
When going outside at night, always go with a family member and watch your step in dark places. If you find a star that glows reddish, look at it again after a few days to see if its position has shifted relative to nearby stars. Unlike stars in constellations, planets change their positions little by little.
If you want to consult original sources, the National Astronomical Observatory's calendar wiki "Names of the Days of the Week" has a correspondence table between days and celestial bodies. The row for Tuesday lists the Greek, Latin, and Sukuyokyo names. Since this article is a rephrasing of sources, please compare the details in the original texts.
You can also compare calendars at home. Open several calendars and look at the Tuesday column. Some may have only the character "Fire," some may write "Tuesday," and others may include "Tue" in English. Comparing how the same day is written in different characters and words makes the story of names feel much closer to home.