109. Our Stellar Neighborhood (post 1)

FTL is the break point of science fiction. Without a faster than light drive, exploration is restricted to the local area, and that’s fine with me. I take satisfaction in building planets within the constraints of known stars. But beware, the party is nearly over. We now have the capacity to discover extrasolar planets, and new ones are found every year. Fortunately for latecomers to the planet builders guild, megaplanets are easier to find that Earth sized ones, and NASA keeps cutting funding. Still, it won’t be too many years before you can’t decide for yourself where, within the limits of orbital mechanics, you want the planets of Alpha Centauri or Procyon to be.

When I began world building, the prime reference was How to Build a Planet by Poul Anderson. I also had an article from Sky and Telescope titled Stars Nearer than Five Parsecs. Today the internet provides an embarrassment of riches, including planet building apps. Apps? Where’s the fun in that?

What I am about to present will be old knowledge to some of you, so forgive me. Not everybody can be a nerd on everything. There are plenty of people, including would-be science fiction writers, who only want a primer on the local neighborhood, because their passions lie elsewhere.

What is the star closest to Earth? The sun. That’s a gotcha riddle among middle school students. The sun’s luminosity is generally given as 1.0, which makes the luminosities of other stars easy to understand by simple comparison.

Okay, what star is next closest, Alpha Centauri or Proxima Centauri? The P- word gives it away, but it isn’t really that simple.

Alpha Centauri isn’t a star, it only seems to be one to the naked eye. A moderate telescope resolves that dot in the sky into three dots. Alpha Centauri is a triple star, or maybe  a double star with a third star wandering through the area. Astronomers haven’t decided yet.

Alpha Centauri is the largest “star” in the constellation Centaurus. Centaurus has moved southward since the ancients named it, so that Alpha Centauri is no longer visible from the northern hemisphere. I had to wait decades to see it, on my first trip to Australia. There you don’t look for Centaurus, you look for the Southern Cross, a kite shaped constellation within Centaurus.

Alpha Centauri is just a dot in the sky, but I was thrilled to finally see the star which was the setting for so many science fiction stories from my youth.

The two stars of the binary pair are named Alpha Centauri A and Alpha Centauri B. The third star is sometimes called Alpha Centauri C, but more often Proxima Centauri because it it slightly closer to Earth. Beta Centauri is something entirely different. The second brightest dot in Centaurus, Beta Centauri is a star system 525 light years from Earth – not in the local neighborhood at all. Beginners sometimes say Beta Centauri when they should be saying Alpha Centauri B.

The naming convention is widespread, but not universal. Many stars have names given to them by the ancients. Many more are simply alpha-numeric designations, following the conventions of published star charts or inventories by observatories.

*****

Click here for a Wikipedia article that will list 56 of the nearest stars, followed by maps. The first map will give you some idea of where these stars lie in relation to each other.

Tomorrow we can look at some of the rest of the nearby stars, concentrating on those which might have planets useful for human real estate.

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