Category: White Conté on Black Paper

Crater Burg and Lacus Mortis

By Frank McCabe

Crater Burg is a young, sharp rimmed crater formed less than 900,000 years ago and can be seen resting at the east center of the ancient Lake of Death or Lacus Mortis. This 40 km. crater with its central peak and well defined ejecta apron is in stark contrast to the old pre-Imbrium crater, Lacus Mortis which embraces it. Interesting terracing can be seen clearly in the low sunlight.
The Lake of Death crater is a large one as craters go, nearly 160 km. in diameter. Its features include rilles across the floor, a few of which are fairly long. Perhaps these floor fractures are from doming of the floor as some lava entered from below. The central bulge of this crater can be seen in grazing sunlight much like crater Petavius. Ridges emanating from the northwest and southwest outer walls of Burg can be seen crossing the lake floor all the way to the rim of the Lake of Death. Just to the west of the south ridge of Burg is a straight scarp that continues as a rille as it nears the lake center. It appears much like Rupes Recta. The east face is brightly illuminated by the setting sun near the southern wall of the lake and it is much taller than the more famous straight wall.
Further west on the lava floor is Rima Burg a 100km. long slump in the floor. It is nearly in line with a shadowed valley seen in the hills beyond the boundaries of Lacus Mortis.
Other craters to the east of Burg are superimposed on the old destroyed rim of Lacus Mortis. They are Plana (45 km.) with a central peak sticking up above the lava flooded flat floor and Mason (43 km.) the other crater to the north which is nearly a twin without the central mountain.

Sketching:

For this sketch I used: black Strathmore 400 Artagain paper, 9”x12”, white and black Conte’pastel pencils and a blending stump. Brightness was slightly decreased after scanning.

Telescope: 18 inch f/5 Dobsonian and 9mm eyepiece 222x
Date: 10-30-2007 6:05-7:00 UT
Temperature: 11°C (52°F)
Clear, calm
Seeing: Antoniadi III
Co longitude: 142.8°
Lunation: 19.3 days
Illumination: 75.1 %

Frank McCabe

Wargentin and Environs
By Richard Handy

Immediately south west of Schickard near the South West limb, lies a crater that can truly be regarded as one of the Moon’s most unusual and enigmatic features. Eighty four kilometer Nectarian aged Wargentin is a cup filled to the brim with ancient mare lavas. Its relatively smooth and flat floor has a series of gently sloped branches from it’s central wrinkle ridge, yet beyond this gentle relief it is almost flush with the crater rim, creating a plateau fully 450 meters higher than the surrounding mare. The maria like surface shows significant albedo (shades of grey tone) differences. There is a coating of light material that appears in patches and sheets most probably of Orientale origin, the last remnants of the skirt of fluidized flow fronts settling out over this region.

There are a few smaller or partial versions of this “filled to the rim” crater phenomena on the lunar surface, however nothing of this size appears anywhere else on the Moon. What special conditions must be satisfied to allow for the creation of this bizarre lunar plateau? We can be assured that the inner crater walls did not have many faults or openings that would have allowed the mare lavas to escape. A close look at the exterior wall shows that it remains relatively free of large secondaries or craterlets. This obvious lack of wall destruction certainly must have played a role in the continued embayment of the lavas over time.

An element that may have been a factor was that Wargentin appears have excavated a deep crater in pre-existing mare units. Hypothetically these denser basalt rims could more effectively embay lavas than the rims of craters in plains or highland areas because of their more compact stratification. Rim material would therefore be much more likely to hold the magma within the inner walls, as the floor slowly crept higher and higher on each new inundation.

The third element is perhaps the least well understood. How did its magma channels, cracks or fissures deep beneath the crater bowl itself, feed this unique crater? In other words what kind of plumbing was required to allow this “bathtub” of a crater to fill to overflowing? There must be a reason that the crater continued to fill up over the millions of years required to lay down such a volume of lava. Or alternately did it fill up, at least partially, in a relatively short time span of tens of thousands of years while still a young feature, perhaps after the impact penetrated into liquid magma filled channels or chambers? Nearby Schickard shows evidence that some mare lava flooding occurred after the dusting by the Orientale impact and therefore argues for a gradual buildup over many tens of millions of years.

Lunar geological research will undoubtedly uncover some of the reasons this remarkable and puzzling feature exists, yet its enigmatic and singular nature may well have to wait for a more sophisticated understanding of the early lunar crust and mantle.

Sketch details

Subject: Wargentin and environs
Date: 3-2-07 (UT) Julian date: 3-1-07
Session Start 6:32 UT End 8.00 UT
Seeing: Antoniadi II-III Weather clear
Lunation 1041, 12.51 days Phase: 20.1 deg Illumination 96.9%
Colongitude: 65.0 deg
Lib in Lat: -02 deg 19 min Lib. in Long: +4 deg 52 min
Telescope: Meade 12” SCT f/10
Meade Star diagonal
Binoviewer: W.O. Bino –P with 1.6X nosepiece
Eyepieces: 12.4 mm Meade Super Plossls
Magnification: 393X
Sketch medium: White Conte’ Crayon on black textured Strathmore paper
Sketch size: 18” x 24”

On October 30, site administrator, Rich Handy, lost his home to a fire. He and his family are ok, but as you can imagine he has a lot to deal with right now. Please keep him in your thoughts during this very difficult time. Until Rich feels ready to return to administering the site, I’ll do my best to keep things going. I’ve updated the submission page to include an email address to which I have access.

Rich has been very conscientious about not posting any of his own sketches here. I think this is an appropriate opportunity to dedicate the November 1, 2007 Astronomy Sketch of the Day to one of his many excellent Lunar sketches.

Hang in there Rich, we’re all pulling for you,

Jeremy Perez

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Here are Rich’s notes about the beautiful surroundings of Hainzel, Hainzel A and Hainzel C:

In the south western quadrant of the Moon, amidst the heavily bombarded highland terra and adjacent to Lacus Timoris (the poetically named “Lake of Time”), lies the trio of complex overlapping craters, Hainzel, Hainzel A and C. A quick look at this grouping in this lighting may leave one with the mistaken impression that these three are the result of a single asteriod that broke into a couple of major chunks just prior to impact, resulting in the elongate structure without an obvious wall separating the two larger impacts. Despite that appearance, however, each crater was formed at a different epoch.

78 km Hainzel which comprises a good portion of the southern portion of the “fiddle” shaped complex, is a Nectarian era feature, formed sometime between 3,920 and 3,850 million years ago. In my sketch you can see that indeed, the lower crater has taken several impacts to it’s rim. In contrast, 38 km Haizel A above it, is a relatively youthful Erastosthenian era crater formed between 3,200 and 1,100 million years ago. Here again its youth can be gaged by the very fresh looking glacis, shown in my sketch as the ropey and branching area to the upper right of Hainzel A’s rim (the upper body of the fiddle). The drawing shows few superposed craters over this large area, a definite indicator of freshness. 19 km by 28 km Hainzel C is an Imbrium era crater formed during the gap in time between Hainzel and Hainzel A’s appearance between about 3,800 million and 3,200 million years ago. The light was not favorable for a good look at C, covered as much as it it was by deep shadow from it’s bigger brothers. Hainzel C is superposed on Hainzel. Previous views of C showed a damaged and disrupted floor and walls, most probably the result of the impact of A.

Here are the sketch details:

Subject: Hainzel, Hainzel A and C Rukl: 63
Date: 10-2-06 Time: 4:24 UT-5:43 UT
Seeing: Antoniadi III-IV Weather clear, light breeze
Lunation: 10.65 days Phase: 55.7 deg Colongitude: 39.5 deg
Illumination: 78.2%
Lib in Lat: +4 deg 55 min Lib. in Long: -5 deg 11 min
Telescope: 12″ Meade SCT, f/10
Binoviewers: W.O. Bino-P with 1.6X Nose piece
Eyepieces: 12.4 mm Meade series 4000 Super Plossls
Magnification: 393X
Sketch medium: White and black Conte’ Crayon on black
textured Strathmore paper.
Sketch size: 18″ x 24″