, but is more trustworthy when derived with the
spectroscopic method of ADAMS. It is probable from a discussion of the
_B_-stars, to which we return in a later chapter, that the absolutely
brightest stars have a magnitude of the order -5m or -6m. If the
parallaxes smaller than 0".01 were taken into account we should find that
Canopus would represent the absolutely brightest star, having _M_ =
-8.17, and next to it we should find RIGEL, having _M_ = -6.97, but both
these values are based on an annual parallax equal to 0".007, which is
too small to allow of an estimation of the real value of the absolute
magnitude.

If on the contrary the _absolutely faintest_ stars be considered, the
parallax stars give more trustworthy results. Here we have only to do
with near stars for which the annual parallax is well determined. In
table 8 I give a list of those parallax stars that have an absolute
magnitude greater than 9m.

There are in all 19 such stars. The faintest of all known stars is
INNES' star "Proxima Centauri" with _M_ = 13.9. The third star is
BARNARD's star with _M_ = 11.7, both being, together with [alpha]
Centauri, also the nearest of all known stars. The mean distance of all
the faint stars is 1.0 sir.

There is no reason to believe that the limit of the absolute magnitude
of the faint stars is found from these faint parallax stars:--Certainly
there are many stars in space with _M_ > 13m and the mean value of _M_,
for all stars in the Galaxy, is probably not far from the absolute value
of the faint parallax stars in this table. This problem will be
discussed in a later part of these lectures.

FOOTNOTES:

[Footnote 15: Compare ADAMS' memoirs in the Contributions from Mount
Wilson.]

[Footnote 16: The first line gives the stars of an absolute magnitude
between -4.9 and -4.0, the second those between -3.9 and -3.0, &c. The
stars of type B and A are from WALKEY's catalogue.]

[Illustration: PLATE I.

_CONVERSION OF EQUATORIAL COORDINATES INTO GALACTIC COORDINATES._]

[Illustration: PLATE II.

_Squares and Constellations._]

[Illustration: PLATE III.

_The Harvard Classification of Stellar Spectra._]

[Illustration: Plate IV.

_Distribution of the parallax stars over different absolute
magnitudes._]

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