Last Saturday’s image of Proxima Centauri raised questions for several readers, who asked where Centauri A and B were in the photograph. The answer is that they are not in the field of view. To get a broader perspective, let’s step back a bit. In the image below, I’m using a photograph taken by Noël Cramer at the Observatoire de Genève. I’ve cropped the image to show the relative position of the primary Centauri stars and Proxima Centauri. If you look to the upper right of the image, you’ll see the tip of the red arrow that Cramer used to point to Proxima, which is otherwise indistinguishable.

Now ponder the bright ‘star’ at lower left. It is actually not one but two stars, Centauri A and B. The two are so close to each other, and so close to us, that they effectively merge into a single image, which is why we talk about ‘Alpha’ Centauri — it was once thought to be simply the single brightest star in the Centaur constellation. Now, of course, we know it is a triple system, with the two major stars both Sun-like and theoretically capable of supporting an Earth-like planet in their respective habitable zones.

Consider the distance between the bright Centauri A and B duo and Proxima in the above image. You’re looking at 10,000 AU, about the distance between the Sun and the Oort Cloud in our own Solar System.

Let’s back out to see a fuller view of the Cramer photograph. Now we see a second bright star at the top of the image. This is Beta Centauri. Despite the confusing nomenclature, Beta Centauri is not part of the Alpha Centauri triple star system. In other words, it’s not Centauri B; it’s merely the second brightest star in the Centaur. Alpha Centauri is the ‘star’ at the bottom, and if you look at about the 2 o’clock position at the very edge of the image, you’ll see just the tip of the red arrow that Cramer used to mark Proxima Centauri.

One thing that would surely galvanize the interstellar effort is the discovery of a terrestrial world around one of the Centauri stars. If such a blue and green world swam into view one day (perhaps through the efforts of the Terrestrial Planet Finder mission), reaching another star would be elevated to serious consideration by the various agencies that map out future space missions. Perhaps more important, however, would be the energizing effect on a public that has grown all too blasé about breakthroughs in the cosmos.

Image credits: Noël Cramer, Observatoire de Genève.