Astrophoto: Plato and the Alpine Valley by Mike Salway
Written by R. Jay Gabany
For many years, there were three popular theories that tried to explain why Earth's satellite hangs in our skies. One postulated that the Moon separated from Earth during our planet's formation, another stated that it was captured when passing close by, and the third held that it formed in place with our planet out of the same material circling the Sun at the solar system's birth. Each of these ideas had their own justifications but none of them provided all of the answers because each of them were well conceived, but, educated guesses.
Scientists have learned much about the Moon's composition through direct analysis of rocks that were returned by the NASA Apollo Moon landing missions. Based on the examination of lunar material, a fourth theory emerged and gained credence- the Moon formed when our world was hit by another body, roughly the size of Mars! This event is believed to have occured over four billion years in the past when the Earth was new, barely 50 million years old. The material ejected from this world shattering collision eventually coalesced to form our planet's orbiting minion. This early period was then followed by a heavy bombardment of projectiles that rained down over hundreds of millions of years to form the current lunar landscape, part of which is pictured here.
The Moon has always held our fascination. For centuries it represented things beyond our grasp, wholly unattainable, completely impossible or totally insane. Our language is filled with these references. Consider the word lunatic or the metaphor about asking for everything including the Moon. These references still remain part of our common lexicon. Old expressions have a way of persisting in face of current facts. However, since the late 1960's, the Moon has come to symbolize something different. Now, it also conjures visions of determination, surmounting overwhelming odds, heroic undertakings and to some, nostalgia.
The Moon is no longer unattainable. Twelve individuals have visited our natural satellite. During their voyage, the Moon became a place instead of a thing and through their accomplishments we now share that perspective. They explored the Moon at six different locations; skipped and bounced as a substitute for walking; drove vehicles for miles across its powdery surface; gazed up at our world hanging perilously against the black of forever and returned with rocks as souvenirs, like many Earth-bound travelers. In fact, the astronauts brought back lots of rocks- almost half a ton! The rocks have given up their secrets and spoken of a time when the Moon was much younger. While none of them were collected from the area shown in the accompanying picture, they have helped science piece together the fabric of this scene's past.
This picture is of a place located in the northern section of the Moon and to the left of it's center, as seen from Earth. We are looking down on the dark-floored crater named Plato, in the upper left, the lunar Alps, that arc across the image to the right and the Alpine Valley, that cuts a swath through these mountains.
Based on samples returned by Apollo 15, the mountain range was created almost four billion years ago (about half a billion years after the Moon's formation) when a large object slammed into the surface and carved a gigantic impact basin called Mare Imbrium. The mare's mostly smooth lava flooded floor is seen in the lower, mid portion of this image. About a billion years later, an object crashed into the mountains and created the 60-mile wide Plato crater. Plato also filled with molten material leaving its floor relatively flat. The apparent smoothness of the crater's interior contrasts with the jagged one-mile high peaks that surrounds it. The Alpine Valley is about six miles at its widest, ninety-three miles in length and was probably formed due to a fault triggered by the Mare Imbrium-forming impact. The valley subsequently filled with volcanic material following it creation. Note the small rille running down its center- its visibility is an indication of this picture's fine resolution. Similar valleys are occasionally seen at other large impact basins on the Moon.
Plato has been the site of numerous Transient Lunar Phenomenon reported by visual observers. For example, the number and size of small craters seen across its floor has supposedly changed, the floor has grown lighter then darker according to come claims, and mists have also been reported. Each of these incidents have been investigated, all lack photographic or independently measurable proof therefore none have been vetted as accurate. Most have been attributed to seeing conditions here on Earth. Seeing is a term that describes the calmness of the Earth's atmosphere through which we peer at objects located in space. The best seeing conditions are when the air above the observer is calm. Poor seeing is caused by turbulence in the upper atmosphere and is recognizable when the stars are twinkling. Poor seeing causes astronomical objects to appear agitated and blurry and that can sometimes trick the observer into seeing something that really isn't there.
This amazing picture was not taken by a spacecraft in lunar orbit. It was produced from the surface of Earth by Australian astronomer Mike Salway at his observing location in Wyoming, New South Wales. This picture is actually a mosaic of many images that have been stitched together. Mike produced the images combined to form this view on August 3, 2006 through a ten-inch telescope and a hi-resolution video camera.
Do you have photos you'd like to share? Post them to the Universe Today astrophotography forum or email them, and we might feature one in Universe Today.
Written by R. Jay GaBany
Filed under: Astrophotos
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