Pickering's plates) is varied in _s_ by the marked character of the K
line. The spectrum of its fellow traveler (No. 25) is still
undetermined.
It is improbable, however, that even these nearer stars are
practicable subjects for the direct determination of annual parallax.
By indirect means, however, we can obtain some idea of their distance.
All that we want to know for the purpose is the _rate_ of the sun's
motion; its _direction_ we may consider as given with approximate
accuracy by Airy's investigation. Now, spectroscopic measurements of
stellar movements of approach and recession will eventually afford
ample materials from which to deduce the solar, velocity; though they
are as yet not accurate or numerous enough to found any definitive
conclusion upon. Nevertheless, M. Homann's preliminary result of
fifteen miles a second as the speed with which our system travels in
its vast orbit inspires confidence both from the trustworthiness of
the determinations (Mr. Seabroke's) serving as its basis and from its
intrinsic probability. Accepting it provisionally, we find the
parallax of Alcyone = about 0.02', implying a distance of
954,000,000,000,000 miles and a light journey of 163 years. It is
assumed that the whole of its proper motion of 2.
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