nd Observatory, or from the original to
plate I at the end, allowing the conversion of the equatorial
coordinates into galactic ones. The values of [pi] are generally taken
from the table of KAPTEYN and WEERSMA mentioned in the previous chapter.
The values of [mu] are obtained from B. P. C., those of the radial
velocity (_W_) from the card catalogue in Lund already described.

There are in all, in the sky, 20 stars having an apparent magnitude
brighter than 1m.5. The brightest of them is _Sirius_, which, owing to
its brilliancy and position, is visible to the whole civilized world. It
has a spectrum of the type A0 and hence a colour-index nearly equal to
0.0 (observations in Harvard give _c_ = +0.06). Its apparent magnitude
is -1m.6, nearly the same as that of Mars in his opposition. Its
absolute magnitude is -0m.3, _i.e._, fainter than the apparent
magnitude, from which we may conclude that it has a distance from us
smaller than one siriometer. We find, indeed, from the eighth column
that _r_ = 0.5 sir. The proper motion of Sirius is 1".32 per year, which
is rather large but still not among the largest proper motions as will
be seen below. From the 11th column we find that Sirius is moving
towards us with a velocity of 1.6 sir./st. (= 7.6 km./sec.), a rather
small velocity. The third column shows that its right ascension is 6h
40m and its declination -16 deg.. It lies in the square GD_7 and its
galactic coordinates are seen in the 5th and 6th columns.

The next brightest star is _Canopus_ or [alpha] Carinae at the south sky.
If we might place absolute confidence in the value of _M_ (= -8.2) in
the 12th column this star would be, in reality, a much more imposing
apparition than Sirius itself. Remembering that the apparent magnitude
of the moon, according to Sec.6, amounts to -11.6, we should find that
Canopus, if placed at a distance from us equal to that of Sirius (_r_ =
0.5 sir.), would shine with a lustre equal to no less than a quarter of
that of the moon. It is not altogether astonishing that a fanciful
astronomer should have thought Canopus to be actually the central star
in the whole stellar system. We find, however, from column 8 that its
supposed distance is not less that 30 sir. We have already pointed out
that distances greater than 4 sir., when computed from annual
parallaxes, must generally be considered as rather uncertain. As the
value of _M_ is intimately dependent on that of _r_ we must consider
specul