The elements of astronomy; a textbook . of the sur-face ; they seem to bedeep cracks in the crustof our satellite. Mostcurious of all are thelight-colored streaks orrays which radiatefrom certain of the cra-ters, extending in somecases a distance ofmany hundred are usually fromfive to ten miles wide,and neither elevatedor depressed to any considerable extent with reference to thegeneral surface. Like the clefts, they pass across valley andmountain, and sometimes through craters, without any changein width or color. No thoroughly satisfactory explanation hasever been given, though t
The elements of astronomy; a textbook . of the sur-face ; they seem to bedeep cracks in the crustof our satellite. Mostcurious of all are thelight-colored streaks orrays which radiatefrom certain of the cra-ters, extending in somecases a distance ofmany hundred are usually fromfive to ten miles wide,and neither elevatedor depressed to any considerable extent with reference to thegeneral surface. Like the clefts, they pass across valley andmountain, and sometimes through craters, without any changein width or color. No thoroughly satisfactory explanation hasever been given, though they have been ascribed to a staining ofthe surface by vapors ascending from rifts too narrow to be visible. The most remarkable of these ray systems is the one connectedwith the great crater Tycho, not very far from the moons southpole. The rays are not very conspicuous until within a few daysof full moon, but at that time they and the crater from which theydiverge constitute by far the most striking feature of the whole — Archimedes and the Apennines (Nasmyth). § 170] LUNAR MAPS. Ill 170. Lunar Maps. — A number of maps of the moon have beenconstructed by different observers. The most recent and extensive isthat by Schmidt of Athens, on a scale 7 feet in diameter: it waspublished by the Prussian government in 1878. Of the smallermaps available for ordinary lunar observation, perhaps the best isthat given in Webbs Celestial Objects for Common new photographic, large-scale, lunar maps have lately beenpublished, from negatives made at the Lick and Paris observatories. 171. Lunar Nomenclature. — The great plains upon the moonssurface were called by Galileo oceans or seas (Maria), for hesupposed that these grayish surfaces, which are visible to the nakedeye and conspicuous in a small telescope, though not with a large one,were covered with water. The ten mountain ranges on the moon are mostly named after ter-restrial mountains, as Caucasus, Alps,
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