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The Moon is Earth’s only satellite.
It is a cold, dry orb whose surface is
studded with craters and strewn with
rocks and dust called regolith. The
moon has no atmosphere. Recent
lunar missions indicate that there
might have been some frozen ice at
• The same side of the moon always faces
• July 20, 1969 – first walk of man on the
moon (Neil Armstrong, Buzz Aldrin &
Michael Collins) aboard Apollo 11.
• The moon is about 238, 900 miles
(384,000 km) from Earth on average.
• Lunar perigree – 221, 463 mi
• Apogee – 252, 700 mi
• Revolution – 27 days and 8 hours
• Rotation – 27 days and 8 hours
(synchronous rotation with the Earth)
• The moon’s orbit is expanding over time
as it slows down.
Saros is the roughly 18-year periodic
cycle of the Earth-Moon-Sun system.
Every 6,585 days, the Earth, Moon and
Sun are in exactly the same position.
When there is a lunar eclipse, there
will also be one exactly 6,585 days
The moon's diameter is 2,159 miles
(3,474 km), 27% of the diameter of
the Earth (a bit over a quarter of
the Earth's diameter).
Mass and Gravity
The moon's mass is (7.35 x 10 22 kg), about 1/81
of the Earth's mass.
The moon's gravitational force is only 17% of the
Earth's gravity. For example, a 100 pound (45 kg)
person would weigh only 17 pounds (7.6 kg) on
The moon's density is 3340 kg/m 3. This is about
3/5 the density of the Earth.
The temperature on the Moon ranges
from daytime highs of about 130°C =
265°F to nighttime lows of about -
110°C = -170°F.
The moon has no atmosphere. On the
moon, the sky is always appears dark,
even on the bright side (because there
is no atmosphere). Also, since sound
waves travel through air, the moon is
silent; there can be no sound
transmission on the moon.
Mare (plural maria) means "sea," but maria
on the moon are plains on the moon. They are
called maria because very early astronomers
thought that these areas on the moon were great
seas. The first moon landing was in the Mare
Tranquillitatis (the Sea of Tranquility). Maria are
concentrated on the side of the moon that faces the
Earth; the far side has very few of these plains.
CRATERS AND RILLES
Craters range in size up to many
hundreds of kilometers, but the most
enormous craters have been flooded
by lava, and only parts of the outline
are visible. The biggest intact lunar
crater is Clavius which is 100 miles
(160 km) in diameter.
A rille is a long, narrow valley on the
surface of the moon. Hadley Rille is a long
valley on the surface of the moon. This rille
is 75 miles (125 km) long, 1300 feet (400
m) deep, and almost 1 mile (1500 m) wide
at its widest point. It was formed by
molten basaltic lava that carved out a
steep channel along the base of the
Apennine Front (which was explored by the
Apollo 15 astronauts in 1971).
Libration is a rocking movement of the Moon.
Librations cause us to view the Moon from
different angles at different times, enabling us to
see about 59 percent of the Moon's surface
from Earth. There are librations due to
variations in the rate of the Moon's orbital
motion (longitudinal libration) and to the
inclination of the Moon's equator with respect
to its orbital plane (latitudinal libration).