THE NEAREST STARS
Of especial interest are the few stars that we know are the nearest to
us, and the following table includes all those whose parallax is 0".20
or greater. There are nineteen in all and nearly half of them are binary
systems. The radial motions given are relative to the sun. The
transverse velocities are formed by using the measured parallaxes to
transform proper motions into linear measures. They are given by
Eddington in his "Stellar Movements":
Column Key
====================
A) Magnitude
B) Parallax in Seconds of Arc
C) Proper Motion in Seconds of Arc
D) Linear Velocity Km. per sec.
E) Radial Velocity Km. per sec.
F) Spectral Type
G) Luminosity (Sun=1)
H) Star Stream
====================================================================
Star's Name | A | B | C | D | E | F | G | H
---------------+-----+------+------+-----+-----+------+-------+-----
Groombridge 34 | 8.2 | 0.28 | 2.85 | 48 | .. | Ma | 0.010 | I
Eta Cassiop | 3.6 | 0.20 | 1.25 | 30 | +10 | F8 | 1.4 | I
Tau Ceti | 3.6 | 0.33 | 1.93 | 28 | -16 | K | 0.50 | II
Epsilon Erid | 3.3 | 0.31 | 1.00 | 15 | +16 | K | 0.79 | II
CZ 5h 243 | 8.3 | 0.32 | 8.70 | 129 |+242 | G-K | 0.007 | II
Sirius |-1.6 | 0.38 | 1.32 | 16 | -7 | A |48.0 | II
Procyon | 0.5 | 0.32 | 1.25 | 19 | -3 | F5 | 9.7 | I ?
Lal. 21185 | 7.6 | 0.40 | 4.77 | 57 | .. | Ma | 0.009 | II
Lal. 21258 | 8.9 | 0.20 | 4.46 | 106 | .. | Ma | 0.011 | I
OA (N) 11677 | 9.2 | 0.20 | 3.03 | 72 | .. | .. | 0.008 | I
Alpha Centauri | 0.3 | 0.76 | 3.66 | 23 | -22 | G,K5 |{2.0 | I
| | | | | | |{0.6 |
OA (N) 17415 | 9.3 | 0.27 | 1.31 | 23 | .. | F | 0.004 | II
Pos. Med. 2164 | 8.8 | 0.29 | 2.28 | 37 | .. | K | 0.006 | I
Sigma Draco | 4.8 | 0.20 | 1.84 | 43 | +25 | K | 0.5 | II
Alpha Aquilae | 0.9 | 0.24 | 0.65 | 13 | -33 | A5 |12.3 | I
61 Cygni | 5.6 | 0.31 | 5.25 | 80 | -39 | K5 | 0.10 | I
Epsilon Indi | 4.7 | 0.28 | 4.67 | 79 | -62 | K5 | 0.25 | I
Krueger 60 | 9.2 | 0.26 | 0.92 | 17 | .. | .. | 0.005 | II
Lacaille 9352 | 7.4 | 0.29 | 7.02 | 115 | +12 | Ma | 0.019 | I
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These stars are distant less than five parsecs (about 16 light-years)
from the sun, so they make up the closest fringe of the stellar universe
immediately surrounding our system. The large number of binary systems
is quite remarkable. Why some stars are single and others double is not
yet known. By the spectroscopic method the proportion is not so large;
Campbell finding that about one quarter of 1,600 stars examined are
spectroscopic binaries, and Frost two-fifths to a half. The exceptional
number of large velocities is very remarkable; the average transverse
motion of the nineteen stars is fifty kilometers per second, whereas
thirty is about what would have been expected.
As to star streams to which these nearest stars belong, eleven are in
Stream I and eight in Stream II, in close accord with the ratio 3:2
given by the 6,000 stars of Boss's catalogue. "We are not able," says
Eddington, "to detect any significant difference between the
luminosities, spectra, or speeds of the stars constituting the two
streams. The thorough interpenetration of the two star streams is well
illustrated, since we find even in this small volume of space that
members of both streams are mingled together in just about the average
proportion."
[Illustration: THE RING NEBULA IN _Lyra_. This is the best example
of the annular and elliptic nebulae, which are not very abundant.
(_Photo, Mt. Wilson Solar Observatory._)]
[Illustration: THE DUMB-BELL NEBULA OF _Vulpecula_. To take the
photograph required an exposure of five hours. (_Photo, Mt.
Wilson Solar Observatory._)]