It is true that
there are a great many resemblances. a Centauri, our nearest
neighbor, if we can use such a word as "near" in speaking of its
distance, has a spectrum very like that of our sun, and so has
Capella. But even in these cases careful examination shows
differences. These differences arise from variety in the
combinations and temperature of the substances of which the star
is made up. Quite likely also, elements not known on the earth may
exist on the stars, but this is a point on which we cannot yet
speak with certainty.
Perhaps the attribute in which the stars show the greatest variety
is that of absolute luminosity. One hundred years ago it was
naturally supposed that the brighter stars were the nearest to us,
and this is doubtless true when we take the general average. But
it was soon found that we cannot conclude that because a star is
bright, therefore it is near. The most striking example of this is
afforded by the absence of measurable parallaxes in the two bright
stars, Canopus and Rigel, showing that these stars, though of the
first magnitude, are immeasurably distant. A remarkable fact is
that these conclusions coincide with that which we draw from the
minuteness of the proper motions.
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