The Moon - BestLightNovel.com
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APPENDIX
DESCRIPTION OF THE MAP
The accompanying map, eighteen inches in diameter, represents the moon under mean libration. Meridian lines and parallels of lat.i.tude are drawn at every 10 deg., except in the case of the meridians of 80 deg. E. and W. longitude, which are omitted to avoid confusion, and as being practically needless. These lines will enable the observer, with the aid of the Tables in the Appendix, to find the position of the terminator at any time required. As astronomical telescopes exhibit objects inverted, maps of the moon are always drawn upside down, and with the right and left interchanged, as in the diagram above, which also shows how the quadrants are numbered.
This circle [drawing of circle], intended to be .15708 in diameter, represents a circle of one degree in diameter at the centre of the map, and as the length of one selenographical degree is 18.871 miles, it represents an area of nearly 280 square miles.
The catalogue is so arranged that, beginning with the W. limb, and referring to the lists under the first and fourth, and the second and third quadrants, all the formations falling within the meridians 90 deg.
to 60 deg., 60 deg. to 40 deg., 40 deg. to 20 deg., 20 deg. to 0 deg.
(the central meridian), and from 0 deg. to 20 deg., and so on, to the E.
limb, will be found in convenient proximity in the text.
In the Catalogue, N. S. E. W. are used as abbreviations for the cardinal points.
