Moon is the earth's only natural satellite. The orbit, relative to the earth's center, is an almost circular ellipse with the earth at one focus.
The average distance from the center of the earth is 238857mi. In the our solar system, there are 30 other satellites, but our moon is larger and more massive than all of them.
The moon's diameter is a little more than one forth of the earth's diameter, (2160 miles) and its mass is about one eightieth, on eigthyth of that of the earth. The moon's gravity is not great enough to retain an atmosphere, and so, there is no air around it.
The moon and the earth revolve together once in 27(( ))1(( ))3(( )) days around a point 2900 miles from the earth's center, and this point revolves around the sun once a year.
Approximately the same hemisphere of the moon is always towards the earth. It contains the dark spots that form the imagined face of the, ``MAN IN THE MOON''. Also certain markings near the edge are visible at time, and turned out of sight at other times
The moon is a dark globe that shines only as it reflects sunlight.
The cycle of its phases from new moon to full, and back to the new again during the lunar month, results from varying amount of the sunlit hemisphere that is presented to the earth as the moon revolves around it. The bright hemisphere is turned away from us at new moon, when it passes between the earth and the sun. It comes more and more into view at the crescent, first quarter, gibbous phases successively, until the round, full, moon appears in the sky. After the full moon; the phases come in reverse order, when the moon overtakes and passes the sun again.
In addition to the light of the sun which the moon recieves directly, it is also illuminated by sun light reflected from the earth. Earth light on the dark part of the moon is a familiar sight at the crescent phase, when the earth is in the lunar sky and shows nearly its full phase.
The mount of the moon phases has a length of about 29.5 days.
The surface of the moon is pocked with innumerable craters. These craters range in size from small pits less than 1 ft. in diameter, to walled plains about 150 miles in diameter. The wall's slope is more abruptly to the floor inside, and more gradually to the plain around them. The mountains on the moon are best seen near the terminator, i.e. the line between the moon's dark and light sides.
There, the shadows are long, and the contrast between the mountain and plain is more pronounced. Near the moon's south pole, mountains have high peaks up to 26000 ft.
QUOTED FROM:ِ INTERNATIONALِAMERICANA AND BRITANICA ENCYCLOPEDIA
TRANSLATOR'S NOTE)
