1. How many stars can you see in the Subaru star cluster?
Subaru, located in the Taurus constellation, looks like 6 to 7 stars clustered together to the naked eye [1]. People with good eyesight might see about 8 stars, and with binoculars, they can count up to dozens [2]. The number of visible stars changes depending on a person’s eyesight and how dark the sky is. The name "Mutsuraboshi" (Six-Linked Stars) does not mean that six stars are always visible.
The distance to this star cluster is said to be about 445 light-years according to NASA data, but researchers do not fully agree on this value [3]. For now, it is enough to remember that it is in the 400-light-year range. So, what names did people in the past give to this small cluster?
2. Why was Subaru called "Gojagoja Boshi"?
In the Shizuoka City and Shima areas, the name "Gojagoja Boshi" is introduced as a local term. It is said to be a dialect word that simply turned the impression of stars appearing in a cluster into sound [4]. This example is listed in Nojiri Hōei’s *Dictionary of Japanese Star Names*. This dictionary classified about 900 star names that remained in rural, mountain, and fishing villages in Japan; the original work was published in 1973 [4].
In Japan, there are other names like "Mutsuraboshi" (Six-Linked Stars) and "Murikabushi" (Cluster Stars) in the Okinawa region [1][5]. In China, it was called "Mao Xiu," and in Greek mythology, it was called the "Seven Sisters" [5]. Some names focus on stars being clustered, others on being linked, and others on being in a group. Each name highlights a slightly different point of interest. So, when did the most famous name, "Subaru," start being used?
3. How did Sei Shonagon mention Subaru in The Pillow Book?
*The Pillow Book* contains the line: "Stars: Subaru. Altair. Evening star..." [6]. The official FAQ of the Subaru Telescope also cites this passage to explain the origin of the name "Subaru" [6]. Junichi Arimoto from the Kyoto University Hanayama Observatory notes that in this passage, stars are treated as objects of appreciation that are "okashi" (interesting or charming) [7]. Arimoto states that the history of Japanese people appreciating stars is about 1,000 years [7]. However, this is Arimoto’s view, as star-related words appear in poems from even earlier times.
As a literary example of "Subaru," the name "Subaru" (written as 須波流) appears as the Japanese name for the Pleiades in Minamoto no Shitagō’s *Wamyō Ruijushō* [7]. The star entries in this book were still few, including the Sun, Moon, Stars, Morning Star, Altair, Vega, Meteors, and the Milky Way [7]. In an era with few star names, Subaru was included, and Sei Shonagon listed it first. What did this word mean?
4. What does the word "Subaru" mean?
The National Astronomical Observatory’s calendar Wiki states that the etymology of Subaru comes from "sumaru," meaning to gather into one [1]. Kotobank, which compiles dictionaries like the *Seisoban Nihon Kokugo Daijiten*, says the etymology is "suberu hoshi" (stars that are gathered), derived from the six stars appearing gathered as if tied by a string. It also suggests it may have come from "sumaru," which referred to hair or wrist bead ornaments in the past [8].
These are all "theories," and none is definitively proven. Still, the direction of "gathering into one" is common with the names "Gojagoja Boshi" and "Mutsuraboshi" seen in the previous section. So, besides the shape of the cluster, how did Japanese people see other star shapes?
5. How did people in Japan describe the Big Dipper's shape?
In Japan, the Big Dipper is said to look like a "hishaku" (ladle) for scooping water [9]. However, the interpretation is not limited to that. There are also names like "Shiso no Hoshi" (Four-Three Stars), which looked like two dice (with 3 and 4 dots), and "Kajiboshi" (Rudder Star), which looked like a ship’s rudder [10].
The introduction to the *Dictionary of Japanese Star Names* also lists "Kajiboshi" (Rudder Star) as a dialect name for the Big Dipper. The "Ikari Boshi" (Anchor Star) in the Cassiopeia constellation is also introduced alongside it [4]. Names related to ship tools become easier to understand when linked to life by the sea. The Japan Foundation’s materials also introduce the Orion constellation as "Tsuzumi Boshi" (Drum Star) [9]. The same star pattern was seen as a water-scooping tool, a play tool, or a ship part. These interpretations arose in various places. One of these names is now used in an unexpected place.
6. Why was "Subaru" chosen as the name of a telescope?
Near the summit of Mauna Kea on the Big Island of Hawaii, the National Astronomical Observatory has a large optical and infrared telescope. The diameter of its main mirror is 8.2 meters [12]. Its name is the "Subaru Telescope." This nickname was chosen through a public call for names from all over Japan when construction began in 1991. From about 3,500 applications, "Subaru" was selected [6][11].
The name, also known from what Sei Shonagon wrote, was chosen from entries collected nationwide. A small cluster in the night sky saw different names arise in different regions, was written in an essay about 1,000 years ago, and became the name of a telescope.
7. How can you name a star cluster by how it looks?
Today, you can choose one star cluster from an encyclopedia or photo and write down what it looks like in your own words. Naming it by how it looks brings you closer to the thinking behind old names. Remember that people saw the ladle shape not just as a ladle, but also as dice or a rudder. Try seeing the same shape as something else.
If you want to read more, look at the "Stars: Subaru" section of *The Pillow Book*, Nojiri Hōei’s *Dictionary of Japanese Star Names* (original 1973, Tokyo-do Publishing), and the "Frequently Asked Questions" on the Subaru Telescope’s official website.