Just when you think you know . . .

. . . what you are talking about, along come these busybodies with their darned discoveries.;-)

When you're showing people the sky it's fun to point out the North Star, Polaris. People want to be able to find that star with their naked eye, but then it's also interesting to show them Polaris in a telescope. Turns out it's a double star. Cute little blue companion -significantly fainter and off to one side. Well, actually, it's a triple, but the third star is so hard to see it takes something like the Hubble Space Telescope to reveal it.

From that, the standard lecture progresses to the ":fact" that most stars are multiple - some had said up to 80 per cent of the stars have one or more companions orbiting a common center of gravity. What's more, this puts our Sun in the unusual category of being a single star. And if most stars are double, that also raises question about extra-terrestrial life because such multiple systems could raise havoc with the orbits of planets around one or more of the stars - assuming such planets could form.

But now it turns out that one of the more certain "facts" in astronomy - that most stars are doubles - just is not the case. Here's how Sky and Telescope reports the new findings:

January 27, 2006 | Astronomers have known since the 1700s that a significant fraction of stars belong to binary or multiple systems. But what is that fraction? Given the observed fact that most solar-size and larger stars reside in binaries, many astronomers have concluded that more than half of our galaxy's stars belong to multiple-star systems.

But a new study by Charles Lada (Harvard-Smithsonian Center for Astrophysics) shows that conventional wisdom is almost certainly wrong. The problem, says Lada, is that astronomers have neglected to consider our galaxy's most common stellar denizens: red dwarfs (spectral type M). These low-mass, low-luminosity stars make up more than 70 percent of all the stars in the Milky Way.

Lada cites surveys from groups led by Geoff Marcy (University of California, Berkeley), Neil Reid (Space Telescope Science Institute), Xavier Delfosse (Astrophysical Laboratory of Grenoble, France), and others that find that the single-star fraction among red dwarfs is very high. And because red dwarfs are the dominant population of stars, single stars must account for upwards of two-thirds of all stellar systems in the galaxy Lada concludes in his paper, which has been submitted to Astrophysical Journal Letters.

Disturbing? Not really. Truth is, I doubt there has ever been a richer era for astronomical discovery. OK, discoveries were coming fast and furiously when Galileo first pointed his telescope at the night sky - but in between then and now there's been nothing like the stream of discoveries the past decade has brought - IMHO.