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The moon is our planets
only natural satellite. The moon has circled the earth for millions
of years. It is quite probable that if the moon were not there, we
humans would not be here. |
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| Statistics |
| Diameter |
3476 km |
| Distance form Earth |
384,400 km or 221,000 miles |
| Mean orbital velocity |
1.023 km/s or 2,287 mph |
| Surface gravity |
1/6 that of Earth |
| Density |
3.3 water=1 (
3/5 that of Earth) |
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Moon Facts |
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- The Moon orbits around the Earth about once per month. In
fact, the word month actually comes from the word moon.
- The same side of the moon always faces the earth.
- The Moon is moving away from earth at a rate of 1.5
inches per year.
- The moon is not round, but egg shaped with the large end pointed
towards earth.
- The Full Moon always rises at sunset.
- A human first set foot on the Moon on July
20th, 1969. His name was Neil Armstrong.
- The gravitational forces between the Moon and the Earth cause
the tides of the oceans.
- When there are two full moons in one month the second is called
a Blue Moon.
- The apparent size of the moon is the same as the apparent
size of the sun which is why we can have a total eclipse of
the sun.
- The full Moon of each month has a name.
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The gravitational forces between the Earth and the
Moon cause some interesting effects. The most obvious is the tides.
The Moon's gravitational attraction is stronger on the side of the
Earth nearest to the Moon and weaker on the opposite side. Since
the Earth, and particularly the oceans, is not perfectly rigid it
is stretched out along the line toward the Moon. From our perspective
on the Earth's surface we see two small bulges, one in the direction
of the Moon and one directly opposite. The effect is much stronger
in the ocean water than in the solid crust so the water bulges are
higher. And because the Earth rotates much faster than the Moon moves
in its orbit, the bulges move around the Earth about once a day giving
two high tides per day. (This is a greatly simplified model; actual
tides, especially near the coasts, are much more complicated.) |
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The New Moon always rises at sunrise.
And the first quarter at noon.
The Full Moon always rises at sunset.
And the last quarter at midnight. |
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Moonrise takes place about 50 minutes later each day
than the day before.
The new moon can not be seen because the illuminated side faces away from
the earth. This occurs when the Moon lines up between the Earth and the
Sun.
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From Earth, we always see the same side of the Moon.
This "synchronous rotation" is caused by the same force
that causes tides on Earth's oceans -- gravity. The Moon's gravity
pulls on Earth, and Earth's gravity pulls on the Moon.
This gravitational attraction is strong enough to pull the water
in Earth's oceans slightly toward the Moon, creating the tides. Conversely,
Earth's
gravity has slowed down the Moon's rotation on its axis. As a result,
the Moon completes one turn on its axis in the same time it completes
one orbit
around Earth. So the same hemisphere of the Moon always faces Earth. |
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The Earth orbits the sun at a distance of 149 million
kilometers and because the sun's diameter is 134,700 (CHECK THIS)
kilometers, the sun subtends an angle of about 32.5 arc minutes from
the Earth.
The moon orbits the Earth at a distance of 384,500 kilometers
and is 3,476 kilometers in diameter. It also subtends an angle
of about 32.5 arc minutes from the Earth.
These numbers reveal a lucky cosmic coincidence. The sun's diameter
is about 38 times larger than the moon's. But the sun is also
about 38 times farther away than the moon. So their apparent
sizes are just about the same.
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