Sir John Herschel wrote in 1833: “What is the distance of the nearest
fixed star? What is the scale on which our visible firmament is
constructed? And what proportion do its dimensions bear to those of our
own immediate system? To this, however, astronomy has hitherto proved
unable to supply an answer. All we know on this subject is negative.”
To these questions, however, an answer can now be given. Slight
changes of position of some of the stars, called parallax, have been
distinctly observed and measured; and among these stars No. 61 Cygni of
Flamstead’s catalogue has a parallax of 5″, and that of α Centauri has
a proper motion of 4″ per annum.
The same astronomer states that each second of parallax indicates a
distance of 20 billions of miles, or 3¼ years’ journey of light. Now
the light sent to us by the sun, as compared with that sent by Sirius
and α Centauri, is about 22 thousand millions to 1. “Hence, from the
parallax assigned above to that star, it is easy to conclude that
its intrinsic splendour, as compared with that of our sun at equal
distances, is 2·3247, that of the sun being unity. The light of Sirius
is four times that of α Centauri, and its parallax only 0·15″. This,
in effect, ascribes to it an intrinsic splendour equal to 96·63 times
that of α Centauri, and therefore 224·7 times that of our sun.”
This is justly regarded as one of the most brilliant triumphs of
astronomical science, for the delicacy of the investigation is
almost inconceivable; yet the reasoning is as unimpeachable as the
demonstration of a theorem of Euclid.