User Guide

A NEW SUN
As the nearest stellar neighbor of the Sol system, there is a great deal more
data that can be collected about Alpha Centauri than can be amassed about
more remote stars. So far everything we know about Alpha Centauri suggests
that an earthlike world, capable of (at least potentially) supporting human life,
is entirely possible — and perhaps likely.
THE CENTAUR
The earliest astronomers identified groups of stars that seemed to fit togeth-
er, into constellations (“stars together”). The most familiar of these include the
twelve constellations of the zodiac — the constellations through which the Sun
“passes” as the Earth completes its yearly revolution.
About A.D. 135, the Greek astronomer Ptolemy, working in Alexandria, Egypt,
catalogued the twelve zodiacal constellations, plus 36 more. One, just barely
visible on the southern horizon, he listed as Centaurus, the Centaur. Alexandria,
at 31.1° N, is further south than all of Europe and most of North America
(everything but parts of Texas and Florida, and most of Mexico) — no one north
of that point can see the Centaur. In fact, the two brightest stars of this con-
stellation are too far south for even Ptolemy to have seen in Alexandria.
Since none of the well-connected astronomers of ancient times even knew
about these two stars, they never got the individual names that now identify
other bright stars (such as Polaris and Sirius). By the mid-1700s, 40 more con-
stellations had been added to the 48 that Ptolemy had originally catalogued,
and these 88 spanned the heavens. In 1603, Johann Bayer published a cata-
logue, not just of constellations, but of all the brightest stars. The most visi-
ble star in each constellation became “Alpha,” the second-brightest “Beta,”
and so forth. The brightest star in the Centaur became Alpha Centauri. Alpha
Centauri is at the Centaur’s hip.
A NEW SUN
APPENDIX 5
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