This makes its mass to that of our globe about as
1 to 81. In other words, it would take eighty-one moons to
counterbalance the earth. Before speaking of the force of gravity on the
moon we will examine the character of the lunar surface.
To the naked eye the moon's face appears variegated with dusky patches,
while a few points of superior brilliance shine amid the brighter
portions, especially in the southern and eastern quarters, where immense
craters like Tycho and Copernicus are visible to a keen eye, gleaming
like polished buttons. With a telescope, even of moderate power, the
surface of the moon presents a scene of astonishing complexity, in which
strangeness, beauty, and grandeur are all combined. The half of the moon
turned earthward contains an area of 7,300,000 square miles, a little
greater than the area of South America and a little less than that of
North America. Of these 7,300,000 square miles, about 2,900,000 square
miles are occupied by the gray, or dusky, expanses, called in lunar
geography, or selenography, _maria_--i.e., "seas." Whatever they may
once have been, they are not now seas, but dry plains, bordered in many
places by precipitous cliffs and mountains, varied in level by low
ridges and regions of depression, intersected occasionally by immense
cracks, having the width and depth of our mightiest river canons, and
sprinkled with bright points and crater pits. The remaining 4,400,000
square miles are mainly occupied by mountains of the most extraordinary
character.
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