f the chart. I know that
Jupiter is to be looked for about 30 m. east, or to the left, of that
line. At the bottom and top of the chart, every twenty minutes of R.A.
is indicated, so that it is easy, with the eye, or with the aid of a
ruler, to place the vertical line at some point of which Jupiter is to
be found.

[Illustration: CHART NO. 5.--FROM RIGHT ASCENSION 16 HOURS TO 20 HOURS;
DECLINATION 10 deg. NORTH TO 30 deg. SOUTH.]

Then I consult my note of the declination of the planet. It is south
23 deg. 20 min. On the vertical borders of the chart I find the figures of
the declination, and I observe that 0 deg. Dec., which represents the
equator of the heavens, is near the top of the chart, while each parallel
horizontal line across the chart indicates 10 deg. north or south of its
next neighbor. Next to the bottom of the chart I find the parallel of
20 deg., and I see that every five degrees is indicated by the figures at
the sides. By the eye, or with the aid of a ruler, I easily estimate
where the horizontal line of 23 deg. would fall, and since 20 min. is the
third of a degree I perceive that it is, for the rough purpose of merely
finding a conspicuous planet, negligible, although it, too, can be
included in the estimate, if thought desirable.

Having already found the vertical line on which Jupiter is placed and
having now found the horizontal line also, I have simply to regard their
crossing point, which will be the situation of the planet among the
stars. I note that it is in the constellation Sagittarius in a certain
position with reference to a familiar group of stars in that
constellation, and when I look at the heavens, there, in the place thus
indicated, Jupiter stands revealed.

[Illustration: CHART NO. 6.--FROM RIGHT ASCENSION 20 HOURS TO 24 HOURS
(0 II.); DECLINATION 10 deg. NORTH TO 30 deg. SOUTH.]

The reader will readily perceive that, in a precisely similar manner,
any planet can be located, at any time of the year, and at any point in
its course about the heavens. But it may turn out that the place
occupied by the planet is too near the sun to render it easily, or at
all, visible. Such a case can be recognized, either from a general
knowledge of the location of the constellations at various seasons, or
with the aid of the Nautical Almanac, where at the beginning of each set
of monthly tables in the calendar the sun's right ascension and
declination will be found. In locating the sun, if you f