********** THE MOON ***************
Vijay
The moon is Earth's only natural satellite. The moon 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 be some frozen ice at the poles.
The same side of the moon always faces the Earth. The far side of the
moon was first observed by humans in 1959 when the unmanned Soviet
Luna 3 mission orbited the moon and photographed it. Neil Armstrong
and Buzz Aldrin (on NASA's Apollo 11 mission, which also included
Michael Collins) were the first people to walk on the moon, on July
20, 1969.
If you were standing on the moon, the sky would always appear dark,
even during the daytime. Also, from any spot on the moon (except on
the far side of the moon where you cannot see the Earth), the Earth
would always be in the same place in the sky; the phase of the Earth
changes and the Earth rotates, displaying various continents.
THE MOON'S ORBIT
The moon is about 238,900 miles (384,000 km) from Earth on average. At
its closest approach (the lunar perigee) the moon is 221,460 miles
(356,410 km) from the Earth. At its farthest approach (its apogee) the
moon is 252,700 miles (406,700 km) from the Earth.
The moon revolves around the Earth in about one month (27 days 8
hours). It rotates around its own axis in the same amount of time. The
same side of the moon always faces the Earth; it is in a synchronous
rotation with the Earth.
The Moon's orbit is expanding over time as it slows down (the Earth is
also slowing down as it loses energy). For example, a billion years
ago, the Moon was much closer to the Earth (roughly 200,000
kilometers) and took only 20 days to orbit the Earth. Also, one Earth
'day' was about 18 hours long (instead of our 24 hour day). The tides
on Earth were also much stronger since the moon was closer to the
Earth.
SAROS
The 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 later.
SIZE
The moon's diameter is 2,140 miles (3,476 km), 27% of the diameter of
the Earth (a bit over a quarter of the Earth's diameter).
The gravitational tidal influence of the Moon on the Earth is about
twice as strong as the Sun's gravitational tidal influence. The
Earth:moon size ratio is quite small in comparison to ratios of most
other planet:moon systems (for most planets in our Solar System, the
moons are much smaller in comparison to the planet and have less of an
effect on the planet).
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.
The moon's density is 3340 kg/m 3. This is about 3/5 the density of
the Earth.
TEMPERATURE
The temperature on the Moon ranges from daytime highs of about 130°C =
265°F to nighttime lows of about -110°C = -170°F
ATMOSPHERE
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.
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