Sciency Words: Oh Be A Fine Girl/Guy, Kiss Me!

Sciency Words: (proper noun) a special series here on Planet Pailly focusing on the definitions and etymologies of science or science-related terms.  Today’s Sciency Word is:


Our Sun is a main sequence star, meaning it fuses hydrogen into helium within its core.  The vast majority of stars in the universe are main sequence stars. They’re very important. Unfortunately, the classification system we use for these main sequence stars is a bit odd and not very easy to remember.

The biggest, hottest main sequence stars are called O-type stars.  The smallest and coldest are called M-type stars.  You’d be forgiven for thinking the stars in between are called N-type stars, but no.  Between the letters O and M, we get B, A, F, G, and K-type stars.

Apparently, at least according to Wikipedia, it didn’t start out this way.  Initially, all stars were classified under a different alphabetical system which, I presume, made more alphabetical sense.  But this seems to be yet another case of scientists naming things before those things are properly understood.

In the early 1910’s, Danish astronomer Ejnar Hertzsprung and American astronomer Henry Norris Russell put together what is now known as a Hertzsprung-Russell diagram.  This diagram revealed a close relationship between the color and brightness of most stars.  The color and brightness of these main sequence stars is also closely related to temperature and mass, respectively.

The old system no longer made much sense, but the alphabetical labels had been so widely used in scientific literature that it would have been difficult to get rid of them.  American astronomer Annie Jump Cannon is credited with fixing the problem: she rearranged the old lettering scheme to reflect our new knowledge about stars.  Henry Norris Russell then came up with a handy mnemonic device to help us remember the new system:

I have to admit I’ve always felt like this phrase is a bit pervy.  At least it’s a little more gender inclusive than it used to be (Russell’s original version was “Oh be a fine girl, kiss me,” because obviously astronomers are always male, and obviously males only want females to kiss them—but we’ve moved on from both of those assumptions since Russell’s time).

Still, as a mnemonic device, it works well enough. As I was reading this paper about the search for Earth-like planets, and how various types of main sequence stars might affect those planets, I found myself repeating the “Oh be a fine girl/guy, kiss me!” line quite a lot.  Not out loud, of course.  That would have gotten me slapped by somebody, I’m sure.

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