rge as 7.5 sir. Only [alpha]
Centauri, Sirius, Procyon and Altair lie at a distance smaller than one
siriometer. Of the other stars there are two that lie as far as 30
siriometers from our system. These are the two giants Canopus and Rigel.
Even if, as has already been said, the distances of these stars may be
considered as rather uncertain, we must regard them as being rather
large.

As column 8 shows that these stars are rather far from us, so we find
from column 12, that their absolute luminosity is rather large. The mean
absolute magnitude is, indeed, -2m.1. We shall find that only the
greatest and most luminous stars in the stellar system have a negative
value of the absolute magnitude.

The mean value of the proper motions of the bright stars amounts to
0".56 per year and may be considered as rather great. We shall, indeed,
find that the mean proper motion of the stars down to the 6th magnitude
scarcely amounts to a tenth part of this value. On the other hand we
find from the table that the high value of this mean is chiefly due to
the influence of four of the stars which have a large proper motion,
namely Sirius, Arcturus, [alpha] Centauri and Procyon. The other stars
have a proper motion smaller than 1" per year and for half the number of
stars the proper motion amounts to approximately 0".05, indicating their
relatively great distance.

That the absolute velocity of these stars is, indeed, rather small may
be found from column 10, giving their radial velocity, which in the mean
amounts to only three siriometers per stellar year. From the discussion
below of the radial velocities of the stars we shall find that this is a
rather small figure. This fact is intimately bound up with the general
law in statistical mechanics, to which we return later, that stars with
large masses generally have a small velocity. We thus find in the radial
velocities fresh evidence, independent of the distance, that these
bright stars are giants among the stars in our stellar system.

We find all the principal spectral types represented among the bright
stars. To the helium stars (B) belong Rigel, Achernar, [beta] Centauri,
Spica, Regulus and [beta] Crucis. To the Sirius type (A) belong Sirius,
Vega, Altair, Fomalhaut and Deneb. To the Calcium type (F) Canopus and
Procyon. To the sun type (G) Capella and [alpha] Centauri. To the K-type
belong Arcturus, Aldebaran and Pollux and to the M-type the two red
stars Betelgeuze and Antares.