According to the Royal Astronomical Society of Canada "Observer's Handbook" for 2009, there are 51 single stars, 17 double stars, and 5 triple stars within 18.82 light-years of our solar system. One hundred stars in all. There are probably other very faint red and brown dwarfs within this volume as well (this catalogue is updated every year), and several of these stars are known to have planets, but this list is probably a good look at the solar neighborhood and as complete as could be hoped for at this stage of development of astronomy--roughly a hundred stars within 20 lightyears of home.

This is the volume of space I will call "the Solar Neighborhood", the nearby stars which will be potential destinations for our Project Enterprise probes. An examination of the properties of these objects is a good look at a typical volume of space, and perhaps give some clue as what we can expect when we start sending out robot spacecraft into nearby space. It might be well to keep in mind what a tiny piece of the galaxy this is--the Milky Way is a 100,000 ly across, and a 1000 ly thick at the sun's location, which lies about 30, 000 ly from the galactic nucleus. So it is fairly clear that even the ambitious program of exploration proposed by Project Enterprise only has the task of getting the soles of our feet wet in the cosmic sea. Our sun is near the middle of the galactic disk, that is, we are about 500 ly from its top and bottom surfaces. So the sphere of mapped space we call the Solar Neighborhood is just a speck in the grand scheme of things.

The stellar sample here is quite typical. Although our sun is in the middle of the brightness and mass range for stars, it is still much brighter and much more massive than the typical star. Of the 100 stellar objects in our neighborhood, only 4 are intrinsically brighter than our sun's absolute magnitude of 4.85. These are Alpha Centauri A (M = 4.34, 4.4 ly), Sirius A (M = 1.45, 8.6 ly), Procyon A (M = 2.68, 11.41 ly) and Altair (M = 2.2, 16.78 ly). Remember, magnitude is a logarithmic, not linear, relation. The common log of the the light intensity ratio is 0.4 times the magnitude difference. So Sirius is almost 23 times brighter than our sun. The majority of the stars on the list are faint red dwarfs, Proxima Centauri, the closest star to our sun at 4.22 ly, M = 15.45, being fairly representative. Another commonly cited example is Barnard's Star, M = 13.24, 5.94 ly. Clearly, these are very faint stars, our sun is much brighter than most of its neighbors.

Of the stars we would consider to be roughly comparable to our sun, spectral class F, G and K subdwarfs, there are only a handful: Alpha Centauri A and B, Epsilon Eridani, Tau Ceti, 61 Cygni A and B, Epsilon Indi A, BD +50 1725, Omicron 2 Eridani A, 70 Ophiuchi A and B and Sigma Draconis. Note that of this list, 8 are members of multiple star systems. The closest of these systems is the Alpha Centauri system, at 4.4 ly. The furthest is Sigma Draconis at 18.8 ly.

So at our disposal we have a rather small scattering of dismal little islands scattered about our tiny backyard patch of the cosmic ocean. It's somewhat reminiscent of the choices of destinations our ancient Greek ancestors had when they first ventured out in their flimsy black ships onto the wine-dark sea.