27 November 2014
The Short Answer (TSA)
Craters
The moon has craters. These “surface irregularities” form the rough
surface that gives the face of the moon . . . its “character.” I suppose, if wrinkles give a face character,
craters can give the moon’s face character.
And, in fact, the craters do just that.
The face of the “Man in the Moon,” so popular throughout the centuries,
is nothing more than a shape “seen” by viewers, which is formed by the
irregularities in the surface of the moon.
In 1609,
Galileo built his first telescope, turned it towards the moon and discovered
craters. Meteors, giant rocks hurling
through space, were always suspected to be the cause of the craters. Meteors have and continue to strike the moon
regularly. But, through the centuries,
some believed that volcanic eruptions caused craters. For a period of about 50 years, some believed
that the moon’s surface was covered with ice, and glacial activity caused
craters. Then, the Apollo missions
gathered data that pretty much confirmed that craters were caused by meteor
strikes.
Large Crater
And the
moon still gets struck pretty hard. The
largest recorded strike on the moon happened on 17 March 2013. The impact and plume of dust from the impact was
visible to the naked eye -- if you happened to be moon-watching at the
time.
The earth
has craters too. But the earth doesn’t
get hit by too many meteors because this planet is protected by its
atmosphere. When meteors enter the
gaseous atmosphere of earth, they experience friction, which creates so much
heat that the meteors not only burn, but usually burn-up completely before
reaching the ground.
It takes a
monster of a meteor to reach the surface and make a noticeable crater on
earth. Any relief map of the state will
show Arizona’s Meteor Crater. Meteors
had hit before, but this wasn’t your average meteor. This easily visible monster of a crater (a
bit under a mile wide) was made by a 160 foot-wide piece of space rock hitting
the earth.
Arizona's Meteor Crater
Even when a rare meteor makes it to the earth’s surface, it’s
usually so small that it hardly leaves a mark at all. Few small craters “last” on the surface
of the earth. Rain, snow, and weather gradually
cause these blemishes to fade away.
But things
are different on the moon. There is no
atmosphere of any kind to protect it from constant blows. So, without any friction, space debris crashes
into the surface of the moon at full speed.
Some of these impacts are from meteors speeding through space on a
collision course with the moon. Other objects
and debris are attracted by the moon’s own gravity with the satillite drawing these blows down onto
itself.
The
complete lack of atmosphere has another effect.
The oldest craters on the moon are about 2 billion years old. And, in those two billion years, they haven’t
changed a bit. There really is no
weathering or erosion on the lunar surface.
The craters from most impacts are preserved intact.
And, we don't want to forget the history of “moon crater naming.”
Giovannie Battista Riccioli named the first crater in 1651 and began a
tradition of crater naming that became so widespread that the International
Astronomical Union took over the regulation and recording of crater names in
1919.
There is a
crater named “Apollo” after the Apollo missions. Inside Apollo are some smaller craters
appropriately named after “absent” American astronauts. Aside from craters, the moon also has some
vast plains with names beginning with the word “Mare” meaning “sea.” The Mare Moscoviense, for example, is dotted
with a few craters named after “absent” Soviet cosmonauts.
Craters are
sometimes named in clusters with the name of one big crater given to the smaller craters surrounding it. For example, the crater Copernicus, is surround by smaller craters named
Copernicus A, Copernicus B, etc. Chains
of craters have names beginning with the word, “Catena,” Latin for chain, such
as Catena Davy.
M Grossmann of Hazelwood,
Missouri & Belleville, Illinois
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