Half-hours with the Telescope

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 the planet's path and the stars, taking the latter either from his maps or from a convenient list of stars.[9] My 'Handbook of the Stars' has been constructed to aid the student in these processes. It must be noticed that old maps are not suited for the work, because, through precession, the stars are all out of place as respects R.A. and Dec. Even the Society's maps, constructed so as to be right for 1830, are beginning to be out of date. But a matter of 20 or 30 years either way is not important.[10] My Maps, Handbook and Zodiac-chart have been constructed for the year 1880, so as to be serviceable for the next fifty years or so.

Next, below the table of the planets, we have a set of vertical columns. These are, in order, the days of the month, the calendar -- in which are included some astronomical notices, amongst others the diameter of Saturn on different dates, the hours at which the sun rises and sets, the sun's right ascension, declination, diameter, and longitude; then eight columns which do not concern the observer; after which come the hours at which the moon rises and sets, the moon's age; and lastly (so far as the observer is concerned) an important column about Jupiter's system of satellites.

Next, we have, at the foot of the first page, the hours at which the planets rise, south, and set; and at the foot of the second page we have the dates of conjunctions, oppositions, and of other phenomena, the diameters of Venus, Jupiter, Mars, and Mercury, and finally a few words respecting the visibility of these four planets.

After the thirty-six pages assigned to the months follow four (pp. 42-46) in which much important astronomical information is contained; but the points which most concern our observer are (i.) a small table showing the appearance of Saturn's rings, and (ii.) a table giving the hours at which Jupiter's satellites are occulted or eclipsed, re-appear, &c.

We will now take the planets in the order of their distance from the sun: we shall see that the information given by the almanac is very important to the observer.

Mercury is so close to the sun as to be rarely seen with the naked eye, since he never sets much more than two hours and a few minutes after the sun, or rises by more than that interval before the sun. It must not be supposed that at each successive epoch of most favorable appearance Mercury sets so long after the sun or rises so long before him. It would occupy too much of our space to enter into the circumstances which affect the length of these intervals. The question, in fact, is not a very simple one. All the necessary information is given in the almanac. We merely notice that the planet is most favorably seen as an evening star in spring, and as a morning star in autumn.[11]