Wednesday 20 July 2016

Schickard & Bailly - ancient features prove most intriguing

Hello everyone,

Finally another break in this run of poor weather for a visit to the Moon.

And two consecutive nights too!

As things have transpired, the last few visits to the Moon for me have been close to the Full Moon phase.  Not a complaint, just an observation on the coincidence.  For me, ANY time I get with the Moon of late is welcome.

Both sketches I managed were of very ancient features on the Moon.  So both show their age with their own set of tell-tale features.  And each also offered different sets of features that made each appealing to work on.

The first piece was centred on the ancient crater Schickard.  Schickard is just about a ghost crater now.  Having being formed long ago when the Moon’s crust was thin, the impact saw most of the crater filled in with lava, leaving just the rim.  But today this rim has been just about totally obliterated from the thunderous shaking and jolts it has experienced over billions of years of subsequent impacts, shaking the rim to almost flat today, with just the flooded crater mostly intact.  Not really surprising though as the rim is essentially just pulverised material with no structural integrity, just like dry sand, and the flooded floor being pretty much just a solid lump of rock.

What is intriguing about Schickard is the patch-work nature of its flooded interior.  From its age, one would expect a uniform colouration of the fill material.  Weathering of the lunar surface happens as a result of solar wind reacting with the material on the lunar surface.  The darker the material, the older it is, as newer impacts throw up fresh, unweathered material.  This is why craters such as Tyco and Copernicus are so bright.  Over time, these too will lose their brilliance.

Yet the fill material of Schickard is varied in colouration.  And there is a clue to the reason for this variation in colour through the internal feature of Schickard 1, a volcano.

Volcanos inside craters is a common feature of ancient, flooded craters.  It tells of continued volcanic activity on the Moon long after the original impact opened the thin crust, and lava filled the hollow.  Schickard’s stained floor, and the volcanic dome, can only mean that there was a significant change in the composition of the lava over subsequent eruptions.  The change in composition then explains the difference in colouration as the solar wind reacts differently with different lava compounds.  Curiously too, Schickard 1, the volcano, is the single brightest feature inside Schickard.  Schickard1 is the bright spot just to the right of centre.

To the South of Schickard is a trio of craters that form a very interesting grouping.  What caught my eye about this grouping is the flooded floors of all three give the impression of being higher than the surrounding moonscape.  According to Virtual Moon Atlas, they are!

Object:  Crater Schickard and surrounds
Scope:  C8, 8” SCT
Gear:  8mm LVW, 250X
Date:  18th July, 2016
Location:  Sydney, Australia
Media:  Soft pastels, charcoal & white ink on A4 black paper.

Twenty two hours later I followed up the Schickard sketch with work of the largest crater on the Moon, Bailly.

What most attracted me to Bailly was the delicate shading and fine lines that riddled the entire circumference of the rim, internal and external.

Bailly sits on the western limb of the Moon.  The result being that it is very foreshortened, and the Moon’s libration altering the amount of foreshortening that is seen.  Its position on the limb is such that the Moon’s libration has Bailly come very close to but not quite disappearing behind the limb.

Bailly’s foreshortening provides for an exquisite range of delicate shading and details along the length of its rime.  And the damaged rim on ends of the major axis provide wonderful textures and curving lines as the adjacent moonscape and craters encroach on the rim of Bailly.

The moonscape in front of Bailly is oddly smooth, with a cluster of mid-sized craters providing textural variation.  Despite the similar size of these craters, the age of these craters varies greatly.  Some of these are flooded, while others have clear floors with central peaks.

Object:  Crater Bailly and surrounds
Scope:  C8, 8” SCT
Gear:  8mm LVW, 250X
Date:  18th July, 2016
Location:  Sydney, Australia
Media:  Soft pastels & charcoal on A4 black paper

These two pieces took over two hours each to complete.  A most satisfying few hours spent with the Moon.  I hope you enjoy these pieces too.


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