[3] Up to a short time ago Alpha Centauri was considered the
fixed star nearest to the Sun. By comparing old photographs
of the firmament with such of recent date the renowned
astronomer Barnard found that a very small fixed star--of
the magnitude 10.5 and therefore far from visible to the
naked eye--in the constellation Ophiuchus (Right ascension
17 h. 58 m. 44 s., North declination 4° 27´.4 January 1,
1917) possesses a very large proper motion. It traverses in
a year 10.3 seconds on the firmament. The distance to this
star, which has the largest proper motion so far known,
was later determined to be 3.3 light years or 3/4 of the
distance from Alpha Centauri to our Sun. Hence its velocity
at right angle to the line of vision is computed to be
49 km. (32 miles) per second. Spectroscopic measurements
show that it approaches us with a velocity of 91 km. (56.5
miles) per second along the line of vision. The combined
velocity, therefore, is 103 km. (63 miles) per second, an
unusually high value. The value of 3.3 light years used in
this calculation was determined by the French astronomer
Gonnessiat, who found it by the study of old photographs
from Algeria. He also calculated the parallax of this star
to be 1 second. According to later measurements, given in
the Harvard Bulletins 616 and 617, its parallax is only
0.7 seconds and consequently its distance 4.6 light years
and its speed perpendicularly to the line of vision 70 km.
(43.5 miles) per second. Campbell, in the Lick Observatory,
had determined its radial velocity and found that it
approaches the Sun at the rate of 128 km. (79 miles) per
second. Its total velocity is, according to these two last
determinations, 146 km. (91 miles) per second.
It is by no means improbable that similar discoveries will
be made in the future, so that the Sun will be found to have
more stars in its “immediate” vicinity than previously
assumed.
[4] American and French numeration; the Swedish and English
usage is billion.
The correspondence is indeed surprisingly good. Proportions are, of
course, somewhat different--in particular is the central part of the
Galaxy not so predominating, which fact has been troublesome to the
adherents of the nebula theory. Probably it was originally denser but
has become attenuated through star-formation, explaining, for instance,
the great gap between the constellations Lyra and Vulpecula.
Public-domain text, read in full here on John Shaqi.
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