Saturday 5 May 2018

Crater Humboldt - still so much to learn!

Hi all,

My golly josh!  It has been some 5 months since my last lunar sketch!  This summer has been terrible with astro weather.  Finally there’s been a break in the weather!  Woohoo!

I’ve been wanting to sketch the eastern limb of the Moon from just after the full Moon phase for a very long time.  It is really the only opportunity to sketch features that otherwise are only visible very soon after the New Moon phase, which is not practical being too close to the Sun and the sky is still too bright for good contrast in the image.  On this occasion, the phase was just one day after Full Moon.

It was like looking at the Moon for the very first time!  The whole eastern limb of the Moon is packed full of features that I hadn’t seen before!  It was quite a revelation for me to find out that there was a whole section of the Moon that I was totally unfamiliar with.

This night I took a different approach on what to select to sketch as I couldn’t decide between three or four different areas.   One particular big crater caught my attention, Humboldt.  What most caught my attention is the curious set of central peaks.  So, I looked up Humboldt on the net, and was met with a staggering image from the Lunar Reconnaissance Orbiter – the floor of Humboldt is riddled with a most regular lacy pattern network of riles.  I have never seen such a regular pattern in any crater.  Along with the curious set of central peaks, I was sold on Humboldt as being the center piece of my first lunar sketch in several months.

I was rusty, very rusty to start with.  Not having sketched the Moon for so long, I struggled a little at first to find my grove with the foreshortening and then the shading.  But I persisted and eventually things started to flow and happen a lot more easily.

I found this area quite intriguing.  Humboldt itself is an extremely old feature, yet it’s somehow managed to avoid too much damage over the eons.  Quite remarkable really considering its location so close to the far side of the Moon that has taken the lion’s share of impacts.  Being so close to the limb, and with the terminator just creeping away from the limb, the shadows of the craters, mountains, lone peaks and ridges all made for an outstanding scene and composition to tackle.

While researching this crater after completing the sketch, I came across the site for the Lunar Reconnaissance Orbiter.  The site contains some very high resolution images of Humboldt along with an explanation for the cause of very curious pattern of riles.  As it turns out, these are fracture lines caused by the subterranean magma pressure causing the floor of Humboldt to dome.  From the LROC photograph below, one can see that the pattern of fracture lines is of-center to the geometric center of Humboldt.  This is because the crown of the dome is not centered either.

LROC image.

This sketch was a lovely way to blow the cobwebs out and get back into the grove of some sketching.  Fingers crossed it won’t be another five months until the next!

Object:  Crater Humboldt and surrounds
Telescope:  8” SCT
Gear:  9mm TMB, 222X
Date:  1st May, 2018
Location:  Sydney, Australia

Until next time,

Clear skies and sharp pencils,


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