[Illustration: CHART NO. 3.--FROM RIGHT ASCENSION 8 HOURS TO 12 HOURS; DECLINATION 30° NORTH TO 10° SOUTH.]
Declination (printed D. or Dec.) expresses the distance of a celestial body north or south of the equator of the heavens.
With these explanations we may proceed to find a planet by the aid of the Nautical Almanac and our charts. I take, for example, the ephemeris for the year 1901, and I look under the heading "Jupiter" on page 239, for the month of July. Opposite the 15th day of the month I find the right ascension to be 18 h. 27 m., neglecting the seconds. Now 27 minutes are so near to half an hour that, for our purposes, we may say Jupiter is in R.A. 18 h. 30 m. I set this down on a slip of paper, and then examine the declination column, where I find that on July 15 Jupiter is in south declination (the sign - meaning south, as before explained) 23° 17´ 52´´, which is almost 23° 18´, and, for our purposes, we may call this 23° 20´, which is what I set down on my slip.
[Illustration: CHART NO. 4.--FROM RIGHT ASCENSION 12 HOURS TO 16 HOURS; DECLINATION 10° NORTH TO 30° SOUTH.]
Next, I turn to Chart No. 5, in this chapter, where I find the meridian line of R.A. 18 h. running through the center of 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° NORTH TO 30° SOUTH.]
Then I consult my note of the declination of the planet. It is south 23° 20´. On the vertical borders of the chart I find the figures of the declination, and I observe that 0° 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° north or south of its next neighbor. Next to the bottom of the chart I find the parallel of 20°, 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° would fall, and since 20´ 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.