A Popular History of Astronomy During the Nineteenth Century: Fourth EditionClerke, Agnes M. (Agnes Mary)
History
A Popular History of Astronomy During the Nineteenth Century: Fourth Edition
Clerke, Agnes M. (Agnes Mary)
Astronomy -- History -- 19th century
Thus from three different quarters, three successful and almost
simultaneous assaults were delivered upon a long-beleaguered citadel of
celestial secrets. The same work has since been steadily pursued, with
the general result of showing that, as regards their overwhelming
majority, the stars are far too remote to show even the slightest trace
of optical shifting from the revolution of the earth in its orbit. In
nearly a hundred cases, however, small parallaxes have been determined,
some certainly (that is, within moderate limits of error), others more
or less precariously. The list is an instructive one, in its omissions
no less than in its contents. It includes stars of many degrees of
brightness, from Sirius down to a nameless telescopic star in the Great
Bear;[77] yet the vicinity to the earth of this minute object is so much
greater than that of the brilliant Vega, that the latter transported to
its place would increase in lustre thirty-eight times. Moreover, many of
the brightest stars are found to have no sensible parallax, while the
majority of those ascertained to be nearest to the earth are of fifth,
sixth, even ninth magnitudes. The obvious conclusions follow that the
range of variety in the sidereal system is enormously greater than had
been supposed, and that estimates of distance based upon apparent
magnitude must be wholly futile. Thus, the splendid Canopus, Betelgeux,
and Rigel can be inferred, from their indefinite remoteness, to exceed
our sun thousands of times in size and lustre; while many inconspicuous
objects, which prove to be in our relative vicinity, must be notably his
inferiors. The limits of real stellar magnitude are then set very widely
apart. At the same time, the so-called "optical" and "geometrical"
methods of relatively estimating star-distances are both seen to have a
foundation of fact, although so disguised by complicated relations as to
be of very doubtful individual application. On the whole, the chances
are in favour of the superior vicinity of a bright star over a faint
one; and, on the whole, the stars in swiftest _apparent_ motion are
amongst those whose _actual_ remoteness is least. Indeed, there is no
escape from either conclusion, unless on the supposition of special
arrangements in themselves highly improbable, and, we may confidently
say, non-existent.
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