Why Do Subaru Cars Have a Logo that Seems to Refer to the Star Cluster, the Pleiades?
I always thought that the logo on Subaru cars (we own one) was incorrect in the number of stars shown (there are six: five small ones and one large one). Afterall, in Japan the Pleiades is also known as “Subaru,” and in popular jargon the star cluster is also known as the “Seven Sisters.” The Seven Sisters were part of Greek myth and there were seven stars that they became. (I won’t go into the reasons for that. Google it.) The reason the star cluster was associated with the myth (or vice-versa) was the prominence of seven stars in the cluster that are visible to the naked eye. Unless you live near Los Angeles as I do. I can’t see any of them thanks to the non-star-friendly local governments which do not limit light pollution from streetlights, building lights and residential lights. Actually, unless you have very good eyes you can only see six stars today—even under dark skies. However, in my telescope I can see a lot more than seven. But that is neither here nor there for the present post.
So why did the ancients with normal eyesight name the star cluster Pleiades if they would have only seen six stars? The answer is that back in those days they could see seven stars with the naked eye. And the reason wasn’t because the skies were darker. They were darker, and significantly so, but as with my telescope that is neither here nor there.
Would you believe that one of the seven originally visible to the naked eye has declined in brightness so that it can no longer be seen? Or, would you believe that one of the seven stars has, since Greek or Babylonian times, moved so that it is so close to one of the other seven as to be indiscernible as a separate star? If you believe both of those explanations you get an “A” because both are true. (Of course, in my telescope the two stars in question are both quite distinct from one another. But again, that is neither… Okay, I’ll stop repeating that.)
The star which has declined in brightness is Pleione. And Pleione has also moved! A much brighter star, Atlas, is near Pleione. Over the millennia Pleione has moved closer to Atlas. So, they appear as one.
Why have these two things happened? First the dimming. Pleione is known as a shell star, which apparently is a convenient abbreviation for “a star with an extended atmosphere.”[i] Shell stars have rotationally broadened photospheric spectral lines in combination with very narrow absorption lines. Some stars with “extended atmospheres” rotate so fast as to smear out the light absorption spectrum and are variable in both brightness and spectra.[ii] Moreover the shell features may appear or disappear over time leading to changes in brightness. So, it seems that today Pleione’s shell has led to a dimming compared to the situation in antiquity.
As for the movement of the star—well that happens. Stars are not fixed, no matter what people used to think. Or still do. Stars have what is called “proper motion,” which does not refer to the motion you see on any given night as the hours go by. Or to polite behavior. A typical star has a proper motion of about 0.1 arc-second per year.[iii] That is imperceptible to the casual observer. But over millennia, say 4000 years since the Babylonians did their thing with observing and naming stars, a typical star would have moved (relative to other stars) by one degree, or twice the width of the moon. Very noticeable. Except not, unless someone took a photograph of the sky 4000 years ago and posted it on the internet. Just kidding. However, the constellation shapes that are familiar to us today would have appeared quite different to ancient observers of the skies. Perhaps some of the names of constellations and myths about them that have come down to us would be more understandable if we knew what star configurations looked like that long ago. I have not researched this. Maybe I will someday. Maybe someone else already has.
Now, back to the Subaru automobile. As I stated at the start of this post the Subaru logo (on the front of their cars) has one large star and five smaller ones. The natural interpretation is that the Subaru logo is meant to signify the Pleiades. It’s not and here’s why.
In the West the Pleiades refers to the “Seven Sisters” of Greek myth (as already stated, in case you forgot). In Japan the Pleiades cluster is named Mutsuraboshi (“six stars”) in an eighth-century chronicle of myths. But Western influence has associated the “Seven Sisters” with the Japanese “Subaru,” so the terms are often used interchangeably. They probably shouldn’t be but it’s too late to change that. Things got clearer for me when I found out that in Japanese the word “subaru” means “united.” That probably explains why the Pleiades are called the Subaru in Japan. (Get it? Cluster = united.) But why the car company? The reason the Subaru logo shows one bright star and five smaller ones simply reflects the fact that the origins of the firm was the joining (“uniting”) of five companies to form one large one. So, the name Subaru can refer to the star cluster or to the auto maker, but not to both in the same breath. It wouldn’t be proper.
[i] https://www.cambridge.org/core/services/aop-cambridge-core/content/view/24B431E081CD82ECA7BC7F121B391787/S0074180900011104a.pdf/introductory_address.pdf
[ii] https://en.wikipedia.org/wiki/Shell_star
[iii] https://www.universetoday.com/135453/stars-move-tracking-movements-across-sky/