Friday 15 April 2016

Aristoteles keeps on teaching

Hello everyone,

At long last I’ve managed a lunar sketch again!  As things would have it, two nights and two sketches!

I didn’t have things all my way.  The first sketch was of Lacus Mortis, and it was poetically killed off early…

One thing that I enjoy doing that is part of my sketching ‘process’ is looking up atlases and information about the area that I’ve sketched.  Often when deciding upon a particular feature to sketch, there has been something peculiar about that feature that has caught my attention and imagination.  And often in my research, I come to have my suspicions justified with amazing revelations.  And sometimes, just sometimes, the most amazing and unexpected details.  Lacus Mortis proved to be one of these exciting revelations, despite clouds rolling in to kill off the sketch session early.

Lacus Mortis, the Lake of Death, is an ancient feature.  It was created early in the Moon’s history when the crust was very thin.  A giant asteroid crashed into the thin crust, and instead of forming a crater as we know it, but the entire basin was flooded.  Lacus Mortis is not unique in this way.  All the Maria we see today all have this essentially round circumference and completely flooded basin.  What distinguishes Lacus Mortis form other ‘seas’ is the fractures and faults that crisscross it.

These fractures and faults all have a curious point of convergence – the centrally located crater, Burg.  Burg is also an ancient feature, though much younger than providence of Lacus Mortis.  The floor of Burg is only partially flooded, giving a hint that the Moon was cooler when Burg was formed that the crust was thicker.

Now, while sketching Burg, I noticed something strange about the inside of its wester side.  There appeared to be another wall inside the western rim.  It somewhat looked like the rim had somehow detached, but the rim looked too intact to be damaged.  But seeing was not good enough to allow for more magnification or resolution of this curious feature.

When I looked up Lacus Mortis on Virtual Moon Atlas, the anomaly that I had spotted became apparent.  This ‘detached wall is actually a gigantic set of volcanic domes!

There are a few clues to the origins of this anomalous internal structure of Burg.  You’ll notice that it does not follow the concentric nature of the remnant terraces.  Another distinguishing feature is this area is made up of darker material than the surrounding material.  And a third distinguishing feature we garner from Earth based volcanic domes, like Mt St Helens’ multiple domes inside its massive caldera.

Burg’s isolated location inside Lacus Mortis and lack of significant later impact damage has meant that much of its original ejecta material ray structures have been preserved.  That this ray system is no longer brilliantly while like Copernicus or Tyco is evidence of the solar wind weathering that occurs on the lunar surface.  A large impact on the Moon throws up material that is from deeper layers under the surface, and its appearance is much brighter.  Though there is no atmosphere or weather or water to cause erosion, weathering occurs as the radiation and solar wind from the sun causes changes in the chemical composition of these fresher material that has been thrown up, causing it to darken.  The brilliant ray system of Copernicus and Tyco will also eventually darken and lose its brilliance.

Lacus Mortis’ riles and fault lines are extensive and massive.  One particular fault line rival Rupes Recta for the vertical height differential between the two sections.  This particular fault line runs north-south in the south-western quadrant.  The shadow that is cast westwards is so long, suggesting the massive height differential.

I so wanted to include the surround mountain ranges and peripheral structures around Lacus Mortis, but clouds rolled in, somewhat appropriately killing off the sketching session.

Object:  Lacus Mortis
Scope:  C8, 8” SCT
Gear:  8mm LVW, 250X
Date:  13th April, 2016
Location:  Sydney, Australia
Media:  White and grey soft pastels, charcoal & white ink on A4 size black paper.

The following night I had a second chance for a sketch.  Aristoteles beckoned this time.

Aristoteles is roughly of a similar age and many similar features as Burg.  It lies on the tortured southern shore of Mare Frigoris.  Its floor is only partially flooded – there are smaller craters around Aristoteles that are ghost craters – totally flooded with only the barest of the original rim still showing.  It has also been spared damage from large subsequent impacts.  Also like Burg, much of the remnant ray system structures have been preserved, though now weathered and no longer brilliantly white.

Aristoteles though share one feature with a much younger, though just as massive impact that formed Copernicus.  Surrounding Copernicus is an extensive system of secondary impacts that were formed from the material that had been thrown out from the original impact.  Aristoteles also shares an extensive collar of secondary impacts.  Differentiating Aristoteles and Burg’s collars apart of these secondary impacts is the very extensive within the ray system of Burg.  Many of these secondary impacts are co-linear, radiating out from the centre of Burg, accentuating the appearance & depth of the ray system.  Aristoteles secondary impacts are much further reaching, attesting to the much larger impact that formed Aristoteles.

One interesting feature around Aristoteles is the ancient, flooded & highly damaged crater Mitchell, immediately on Aristoteles eastern rim.  My sketch shows that the western rim of Mitchell has been obliterated by Aristoteles, and its eastern rim is irregular.  Photographs of Mitchell show that its eastern rim has been filled in by material that had been thrown out from the impact that created Aristoteles.

To the south of Aristoteles is the large crater Exudous.

Object:  Aristoteles & surrounds
Scope:  C8, 8” SCT
Gear:  8mm LVW, 250X
Date:  14th April, 2016
Location:  Sydney, Australia
Media:  White & grey soft pastel, charcoal and white ink on A5 size black paper

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