period is one
hundred and forty-five days. U varies from magnitude seven or eight down
to magnitude twelve or under and then regains its light, in a period of
about two hundred and seven days. S is interesting for its brilliant red
color. When brightest, it exceeds the sixth magnitude, but at some of
its maxima the magnitude is hardly greater than the eighth. At minimum
it goes below the twelfth magnitude. Period, three hundred and
seventy-six days.

[Illustration: MAP NO. 10.]

Next east of Virgo is Libra, which contains a few notable objects (map
No. 10). The star alpha has a fifth-magnitude companion, distant about
230", which can be easily seen with an opera glass. At the point marked
A on the map is a curious multiple star, sometimes referred to by its
number in Piazzi's catalogues as follows: 212 P. xiv. The two principal
stars are easily seen, their magnitudes being six and seven and a half;
distance 15", p. 290 deg.. Burnham found four other faint companions, for
which it would be useless for us to look. The remarkable thing is that
these faint stars, the nearest of which is distant about 50" from the
largest member of the group and the farthest about 129", do not share,
according to their discoverer, in the rapid proper motion of the two
main stars.

In iota we find a double a little difficult for our three-inch. The
components are of magnitudes four and a half and nine, distance 57", p.
110 deg.. Burnham discovered that the ninth-magnitude star consists of two
of the tenth less than 2" apart, p. 24 deg..

No astronomer who happens to be engaged in this part of the sky ever
fails, unless his attention is absorbed by something of special
interest, to glance at beta Librae, which is famous as the only naked-eye
star having a decided green color. The hue is pale, but manifest.[3]

[3] Is the slight green tint perceptible in Sirius variable? I am
sometimes disposed to think it is.

The star is a remarkable variable, belonging to what is called the Algol
type. Its period, according to Chandler, is 2 days 7 hours, 51
minutes, 22.8 seconds. The time occupied by the actual changes is about
twelve hours. At maximum the star is of magnitude five and at minimum of
magnitude 6.2.

[Illustration: MAP NO. 11.]

We may now conveniently turn northward from Virgo in order to explore
Booetes, one of the most interesting of the constellations (map No. 11).
Its leading star alpha, Arcturus, is the brightest in the northe