In the science fiction books of my youth, no one ever mentioned heading out into the universe already knowing what planets would be circling the stars they would visit. Even when I began Cyan, no one was thinking like that, so the first thing my explorers do is to map Procyon’s solar system and discover the eponymous planet which they will explore.
Alpha Centauri A is a near twin of our sun, as well as the closest to us. It used to be logical to assume that we will visit there first. That is no longer true. By the time we find the breakthroughs that will allow even relativistic speeds, we will probably have a full inventory of the nearby cosmos, and our first star journeys are likely to be to relatively well known destinations.
I really hate that. What fun would Columbus have had, if he had seen the National Geographic special first?
Where were we? Ah, the neighborhood.
Ignoring the various stellar specks out there, these are the stars we might have interest in, in order of closeness to Earth.
Alpha Centauri – luminosity 1.0 – 4.4 light years from Earth – already covered yesterday.
Sirius – luminosity 23.0 – 8.6 light years from Earth – is the brightest star in the night sky, as seen from Earth, due both to its inherent brightness and to its closeness to us. Sirius is a binary star. Sirius A is extremely bright and hot; Sirius B is a white dwarf.
Epsilon Eridani – luminosity 0.25 -10.5 light years from Earth – is the closest star which has a reasonably well confirmed planet, a giant thought to be about 3.4 AUs out. An AU (astronomical unit) is the distance from the Earth to the Sun, making it ideal for a quick mental picture of distance. The presence of a giant planet at that distance leaves us free to postulate smaller, more human-friendly planets closer in.
Procyon – luminosity 5.8 – 11.4 light years from Earth – is another binary. Procyon A is hot and white (but nowhere nearly as bright at Sirius) with an even fainter white dwarf companion, Procyon B.
Epsilon Indi – luminosity 0.12 – 11.8 light years from Earth – has three-fourths the mass of the sun and a much lower luminosity. Any human-habitable planets would be close in, with a very short year. If it has a decent tilt, its seasons could go by quite rapidly, leading to interesting story possibilities.
Tau Ceti – luminosity 0.36 (newer figures suggest .55) – 11.8 light years from Earth – Tau Ceti is a slightly smaller Sol type star. It is the nearest single star to so resemble our sun.
When I worked out the backstory for Cyan, I only considered stars within 5 parsecs; I will add two more to this list because Gordon Dickson used them in his version of the neighborhood, which we will see in tomorrow’s post.
Altair – luminosity 11 – 16.7 light years from Earth – is a slightly variable blue white star with a rapid rotation (about 9 hours, compared to the sun’s 25 days) which gives a pronounced equatorial bulge.
Fomalhaut – luminosity 16.6 – 25 light years from Earth – is also blue-white with one known planet called Dagon. The size, nature and composition of Dagon is highly controversial, but it seems to be visible to the Hubble telescope only because it is surrounded by a dust cloud many times larger in diameter than the planet itself.