equal (fifth-magnitude) components, both grey. (See Plate 5.)

CHAPTER VI.

HALF-HOURS WITH THE PLANETS.

In observing the stars, we can select a part of the heavens which may be
conveniently observed; and in this way in the course of a year we can
observe every part of the heavens visible in our northern hemisphere.
But with the planets the case is not quite so simple. They come into
view at no fixed season of the year: some of them can never be seen _by
night_ on the meridian; and they all shift their place among the stars,
so that we require some method of determining where to look for them on
any particular night, and of recognising them from neighbouring fixed
stars.

The regular observer will of course make use of the 'Nautical Almanac';
but 'Dietrichsen and Hannay's Almanac' will serve every purpose of the
amateur telescopist. I will briefly describe those parts of the almanac
which are useful to the observer.

It will be found that three pages are assigned to each month, each page
giving different information. If we call these pages I. II. III., then
in order that page I. for each month may fall to the left of the open
double page, and also that I. and II. may be open together, the pages
are arranged in the following order: I. II. III.; III. I. II.; I. II.
III.; and so on.

Now page III. for any month does not concern the amateur observer. It
gives information concerning the moon's motions, which is valuable to
the sailor, and interesting to the student of astronomy, but not
applicable to amateur observation.

[Illustration: PLATE VI.]

We have then only pages I. and II. to consider:--

Across the top of both pages the right ascension and declination of the
planets Venus, Jupiter, Mars, Saturn, Mercury, and Uranus are given,
accompanied by those of two conspicuous stars. This information is very
valuable to the telescopist. In the first place, as we shall presently
see, it shows him what planets are well situated for observation, and
secondly it enables him to map down the path of any planet from day to
day among the fixed stars. This is a very useful exercise, by the way,
and also a very instructive one. The student may either make use of the
regular maps and mark down the planet's path in pencil, taking a light
curve through the points given by the data in his almanac, or he may lay
down a set of meridians suited to the part of the heavens traversed by
the planet, and then proceed to mark in