Japanese Constellations: Star Names, Myths and the Old Calendar

Around the year 1000, Sei Shonagon sat down to list the things she found beautiful and gave the entire night sky one line: as for stars, the Pleiades. No myth, no explanation. The cluster the rest of the world calls the Seven Sisters was simply Subaru, and her readers needed nothing more.

Japanese constellations come in three layers. The oldest are native star names given by farmers and fishermen, like Subaru for the Pleiades and Mitsuboshi for the belt of Orion. Over those sits the Chinese system of 28 lunar mansions, imported with the court calendar in the seventh and eighth centuries. On top is the modern set of 88 constellations used worldwide, which Japanese astronomers translated into names such as Orion-za and Sasori-za.

Japan's astronomical record runs from court diaries to the Subaru Telescope

Native Japanese star names

Before any imported system arrived, people here named the stars they needed. The names describe tools, animals and farm work rather than gods and heroes, which is the clearest difference between Japanese and Greek star lore.

Mitsuboshi, "three stars", is the belt of Orion, and its rising and setting told farmers when to start work in the fields. The same three stars are Karasuki-boshi in some regions, the plow star, named for the shape of the tool. Orion as a whole was Tsuzumi-boshi, the drum star, after the hourglass-shaped hand drum it resembles.

The Pleiades were Subaru, a word meaning gathered together, and the Big Dipper was Hokuto Shichisei, the seven stars of the northern dipper, or simply Nanatsu-boshi. Aldebaran and the Hyades, trailing behind Subaru, were read as a group following the cluster across the sky.

Names like Yowatashi-boshi, the night-crossing stars, belonged to ordinary people rather than to the court, because the stars that mattered most were the ones that told you how much of the night was left. Much of this vocabulary survived only in dialect. The writer Nojiri Hoei spent decades travelling to collect regional star names before they disappeared, and published them in a dictionary of Japanese star names that remains the standard reference.

The 28 lunar mansions

Japan's formal astronomy arrived from China along with Buddhism, kanji and the calendar. The system that came with it divides the sky into 28 lunar mansions, the nijuhasshuku, marked out along the Moon's monthly path rather than the Sun's annual one.

Each mansion was a reference point for tracking the Moon and for dating events, and the court employed specialists to do it. Onmyoji, the officials of the Bureau of Yin and Yang, read the sky for omens as part of their job, and an unexpected comet or eclipse could change the timing of a ceremony or the mood of a reign.

The mansions also carried divination. Because each was linked to a direction, a season and a set of qualities, an emperor's astrologers could argue that a particular day favored a particular action. Astronomy and astrology were not separate disciplines here; they were the same office.

Japan's oldest star map

The evidence for all this is not only written. The Kitora Tomb in Asuka, Nara has a painted ceiling that the Asuka Historical National Government Park identifies as the world's oldest surviving scientific star map, made between the late seventh and early eighth centuries.

The chart shows Chinese-style constellations, including the Big Dipper, laid out with a gold-leaf star on each point. Whoever painted it was working from a real sky model, not decorating a wall, and the tomb is the earliest physical proof that the 28-mansion system had already taken hold in Japan.

Tanabata and the two stars

Vega and Altair sit on opposite banks of the Milky Way through summer

The one piece of Japanese star lore that everyone knows is Tanabata, built on the stars Vega and Altair, as the Japanese Cultural Center of Hawaii recounts. Vega is Orihime, the weaving princess, and Altair is Hikoboshi, the herdsman. Separated across the Milky Way, they meet one night a year, on the seventh day of the seventh month.

The story came from China, but the festival is thoroughly Japanese. People write wishes on strips of colored paper and tie them to bamboo, and towns compete over the scale of their decorations. Most of Japan celebrates on July 7, while Sendai holds the country's largest Tanabata festival in early August, closer to where the date falls in the old lunar calendar.

The stars themselves are easy to find. Vega, Altair and Deneb form the Summer Triangle overhead through July and August, with the Milky Way running between the first two, exactly as the legend describes. For what else is happening at that time of year, see our guide to July events and festivals in Japan.

Seasons, calendars and the Moon

Japan ran on a lunisolar calendar until it adopted the Gregorian system on January 1, 1873. Months began on the new moon, so the full moon always fell mid-month, and an extra month was inserted every few years to stop the seasons drifting.

Inside that calendar sat the 24 solar terms, the nijushi sekki, which divide the year by the Sun's position and still govern the timing of traditional events. Setsubun, the bean-throwing day, falls immediately before risshun, the start of spring, which is why Setsubun moves around the first days of February rather than sitting on a fixed date.

Tsukimi, moon viewing, keeps the old reckoning. The main night is the fifteenth of the eighth lunar month, which lands between mid-September and early October, and the traditional offerings are pampas grass and rice dumplings stacked in a pyramid. A second viewing, thirteen nights later in the ninth month, was considered unlucky to skip if you had watched the first.

Instruments and the first observatory

The Subaru Telescope, named after the Pleiades, is operated by the National Astronomical Observatory of Japan

Japanese astronomers worked with armillary spheres, gnomons and star globes before Western optics arrived. Octants and sextants came in through Dutch traders at Nagasaki, along with the mathematics to use them, and Japanese instrument makers copied and improved on both.

According to the National Astronomical Observatory of Japan, continuous and methodical observations began at the Asakusa Observatory in 1782 under the official astronomer of the shogunate. The Repsold transit instrument, acquired later, became the foundation of modern positional astronomy in Japan.

The line runs unbroken from there to the Subaru Telescope on Mauna Kea, an 8.2-meter instrument named after the Pleiades. The oldest star name in the language now sits on one of the largest single-mirror telescopes in the world.

Stars in poetry, art and religion

Celestial imagery runs through classical Japanese writing. The oldest existing collection of Japanese poetry, as Columbia University's Asia for Educators describes the Manyoshu, contains dozens of poems on the Tanabata stars alone, using the annual meeting as a figure for separation and longing.

Painters and screen makers worked the same material, and the museums that hold those collections show how often the moon and the Milky Way appear as the setting for a human scene rather than as the subject.

Rural Japan still has skies dark enough for the Milky Way to be obvious

In Shinto the sun is the central body: Amaterasu withdraws into a cave, the world goes dark, and her return restores the light. Buddhism brought a cosmology of layered heavens, and with it star worship, including veneration of the pole star as Myoken Bosatsu and of the Big Dipper as a set of protective deities.

Both traditions needed the calendar. Festival dates, purification rites and temple ceremonies were all set by celestial observation, which is why the court's astronomers were as much religious functionaries as scientists. Our guide to Japanese mythology, gods and yokai covers the wider cast of characters.

Martial traditions absorbed the same symbolism. Schools of Japan's ancient martial arts invoked Myoken and the northern dipper in their transmission documents, treating the fixed point of the sky as a model for a fixed mind.

Seeing the stars in Japan today

Light pollution has taken most of the sky from the cities, but not all of it. Bisei in Okayama built its identity on darkness and passed a light-control ordinance in 1989, long before anyone used the phrase dark-sky reserve. Bisei, an official star-watching town, still has some of the clearest skies in the country.

Elsewhere, the high valleys of Nagano, the Iriomote and Ishigaki islands in Okinawa and the interior of Hokkaido all deliver a full Milky Way on a clear, moonless night. In Tokyo you are limited to the planetariums, which are excellent, and to the brightest handful of stars.

If the history is the draw rather than the observing, Asuka is the place to go. The Kitora Tomb's mural museum, the nearby Takamatsuzuka tomb and the stone monuments scattered across the village make a full day, and it is an easy trip from Nara or Osaka.

Our 12-day maximum culture itinerary builds that kind of stop into a route through the old capitals, if you want the shrines, the tombs and the museums without assembling the trip yourself.