User Guide

Saturn, Uranus or Neptune. In fact, once beyond the radius of Mars, the only
stable orbits are those that circle both stars.
Even if neither star would perturb each other’s habitable planets, they would
still be clearly visible. From a planet circling Alpha Centauri A, Alpha Centauri
B would be a tiny, dazzlingly-bright yellow-orange light in the sky. It will be
a tiny dot, but not quite a point, and it would be far brighter than any full
moon — easily bright enough to read by. It would light up the night sides of
any moons in the sky, as Earth does to the Moon’s dark side if you look care-
fully when the Moon is a crescent. Depending on the geometry at any given
time, soon after sunset or before sunrise you night even see “double crescent”
moons! Alpha Centauri C would be just barely visible at darkest night as a red
naked-eye star from either Alpha Centauri A or B.
PLANETOGRAPHY
Both Alpha Centauri A and B can clearly support habitable planets. We are not
currently aware of any planets orbiting either or both of these stars (although
recent investigations using the Hubble telescope suggest that a giant planet
or a brown dwarf — a very small star — is orbiting Alpha Centauri C). However,
let’s assume a habitable planet orbits Alpha Centauri A. It should be named
Chiron, after the wisest of all the mythological Centaurs, and the tutor of
Achilles, Aesculapius and Hercules. However, anyone who lived there for long
might simply call it Planet.
EARTH COMPARISONS
Planet is quite a bit more massive than Earth, with a larger radius. While the
larger radius reduces the effects of gravity a certain amount, Planet’s greater
mass still creates a 30% greater gravitational pull — objects are 30% heavier
on Planet than on Earth. Planet is a bit farther from Alpha Centauri A than
Earth is from the Sun, but Alpha Centauri A is brighter than the Sun, and these
differences offset, so that Alpha Centauri A is almost exactly as bright from
Planet as the Sun is from Earth.
A NEW SUN
APPENDIX 5
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