THE MOON: EARTH'S ONLY SATELLITE

Salient features of the moon, the earth's only satellite,
are as follows:
. The moon is earth's only satellite.
. The mean distance between the earth and the moon
is about 3,85,000 km.
. Moon has a diameter of about 3,480 'km and a mass
1 of about 81 that of the earth.
. The orbit of the moon is elliptical.
. The time taken by the moon to complete one revolution around the earth is 27 days, 7 hours, 43 minutes and 11 1/2 seconds, or about 273 days. (This
period is called sidereal month.)

.The period of moon's revolution of the sun is 29.53 days on an average, and is called synodic month.
. The moon's period of rotation around its axis and revolution round the earth is same.
. Moon at all times keeps the same side towards the
earth.
. The plane of the moon's orbit is inclined at an angle
of 5° 09' to the plane of the ecliptic.
. When the sun and the moon lie on the same side
of the earth, the moon is said to be in conjunction
with the sun.
. When the sun anc:l. the moon are on opposite sides
of the earth, they are sail.:! to be in opposition.
. The major cause of sea-tides is the gravitational pull of the moon. The sun, because of its greater distance from the earth, has a tide-producing power that is only five-elevenths the tide-producing power of the moon.
. When the moon is between the earth and the sun, the position is called the New Moon. On New Moon, the part of the moon facing the earth is in complete darkness. The moon takes different shapes on different days after the New Moon: waxing crescent (after 3 days), first quarter (7th day), waxing gibbuns (10th day), full moon (14th day), and waning gib­bous (17th day), last quarter (21st day), and waning crescent (25th day).