There's an old saying that the moon is made
of green cheese. Of course, that came from a time when people didn't
really know what the moon is made of. Scientists have learned a lot
about the moon in the last fifty years. Most importantly, we've even
traveled to the moon and collected a sample of some of that green
cheese. You know what they found? It's not made of cheese at all!
It's made out of rock.
Scientists have theorized about
the origin of the moon for centuries, and many implausible theories
abound. But there is one very plausible explanation about the birth
of the moon, which not only answers where it came from, but explains
the earth and moon's rotation and current orbit. Called the Big
Impact Theory, it states that the moon was created when
another celestial body about the size of mars crashed into the earth.
It was such a cataclysmic event that the earth swallowed up the body
that crashed into it, absorbing it into its own mass and increasing
it to its current size. Another major side effect of the collision
was the ejection of a large chunk of earth's rock which was sent into
orbit around the earth, becoming its moon.
The rocks that were collected from
the moon have been studied extensively for their mineral composition.
Examination of "moon soil" samples (called
regolith) have revealed some
strikingly similarities to earth's geology. Rocks made of basalt from
volcanic eruptions and minerals, such as plagioclase
feldspar and olivine,
are exactly the kinds of rocks we find here on earth. In striking
contrast to the true soils that we have here on earth, there are no
organic materials in moon dust. Organic materials come from the breakdown
of living things, such as trees and animals. Since there's nothing
living on the moon, the soil is not a true soil like we're used to
here. It's gray with very fine grained particles like sand or even
dust and extremely dry because there is no water on the moon. (Although
scientists have theorized that there is water ice trapped in the polar
regions of the moon). Because the moon has no atmosphere to protect
it from solar
wind, molecules (like hydrogen, helium, neon, carbon
and nitrogen) from the sun impact the moon's surface directly and
are implanted into mineral grains. Scientists estimate that about
50% of the moon's surface composition is oxygen,
bound up in silicate minerals!
The Man on the Moon
Have you ever looked up at the full
moon and seen what looks like a face? You're not alone, as humans
throughout history have also gazed at the very same moon and seen
that same face. Because of its rotation and orbit we have always seen
the same side of the moon, the side with the face. The dark markings
on the moon come from large basins on the surface that were created
when other space objects (meteors and asteroids) crashed into the
moon billions of years ago. The "eyes" of the face even have names;
the right eye is the Imbrue basin,
and the left eye is the Serenitatis
basin. The rest of the features aren't
quite as clearly "drawn", such as a nose and mouth, but most people
would agree that the moon appears to be watching us.
Humans have
been watching the mysterious moon since the beginning of time. Everyone
knows about the moon's existence, but not very many people know much
more about it. For example, here's some really cool factoids about
the moon:
The moon rises and sets
each day as it orbits the earth, even on the nights when there appears
to be no moon
The light of the moon is
actually a reflection of the light from the sun. So on a full moonlit
night, we're actually getting sunlight that's bouncing off the moon
The age of the moon is approximately
4.6 billion years old, about as old the earth
The moon has no water and
no atmosphere, but it does have an iron core (like the earth)
Phases of the
Moon
Full moons are really cool. Why
can't we have them all the time? Why is the moon never the same,
glowing, fully round orb that we
know so well? The four different phases of the moon - first quarter,
full, last quarter, and "new" moon - have to do with the relative
positions of the sun, the moon and the earth in the moon's monthly
orbit of the earth. It can get pretty confusing because of all the
different orbits and rotations; the moon orbiting around the rotating
earth, the earth and moon orbiting around the sun. But remember; the
light of the moon is actually the light of the sun reflecting off
the face of the moon. Check out the cartoon, at left and below, showing
the moon's orbit around the earth. The reason we don't see any light
on the moon during a new moon is because the far side of the moon
is getting all the light, while the side we see is cast completely
in shadow. When we have a full moon it's because the moon is facing
us AND the sun, so we see its light reflected fully. The other phases
are the stages in between
Get
the current phase of the moon, or predict the moon's phase for a given
date
We always see the same side of the
moon. The moon rotates on its axis while orbiting the earth; it just
does one rotation on its axis for each revolution it makes around
the earth, so it keeps the same side facing the earth. There's an
old saying calling the back side of the moon (the side we never see)
the "dark side of the moon", but that's not really true. The next
time you see a "new moon", remember the dark side of the moon is getting
all of the light, we just don't see it from earth.
Read about our Solar
System | Sun | Geologic
History of Earth | Space Sciences
The Universal Attraction
of the Beach
The moon is more than just a really
cool night light for the sky. The gravitational pull of the moon actually
bulges the water in the oceans out from the earth's surface toward
the moon. The gravitational pull on the side of the earth opposite
the moon is not as strong so the oceans unbulge on that side.
This constant push and pull tug-of-war with the oceans by the moon
is what causes the tides at the beach. So the next time you
find yourself standing on a full, moonlight night on the beach, think
about the moon trying to pull the water out of the ocean! If you want
to find out exactly what time high and low tides will be for a certain
beach you plan on visiting check out the NOAA's
Tide Predictor page.
