Tuesday, August 28, 2012

Armstrong crater

Armstrong crater, Sea of Tranquility - LROC Narrow Angle Camera mosaic of Armstrong, the appropriately unassuming 4.2 km-wide crater (before 1970, "Sabine E") 47.1 km northwest of Tranquility Base (or roughly 64 km north by northwest of the much easier to locate landmark crater Moltke) at 1.356°N, 24.941°E.  From a highly reduced combination of sampled lines from LROC NAC M126765005 (LRO orbit 3815, 47 cm resolution from 39.5 km altitude, April 24, 2010) and M172758358 (orbit 10593, 49 cm resolution from 42.6 km altitude, ), both under mid-day full illumination but many lunar days apart [NASA/GSFC/Arizona State University].
The image above does not do justice to the 16000 line by 10000 pixel montage needed to catch all of modest Armstrong crater at the highest resolution possible. Only two people ever had the opportunity to catch such a view, and they were very busy at that brief moment, absorbed with the raw novelty and challenge of arriving at the lunar surface

The information is stored in two standard double 5000 sample by 52224 line LRO NAC photographs now available in the Planetary Data System (PDS).

A new barely-born effort is underway to make the several life-times worth of PDS data more user-friendly. You can call this an experiment, an early part of that effort, and like most experiments it is a failure.

To illustrate that failure better, as an additional tease, below, at full resolution, and at the maximum 580 by 800 window allowable to users of this blog format, is a very small part of that wall-sized product, specifically the part of the Armstrong crater wall at roughly 5 o'clock (or 170° of arc) in the 'thumbnail' above featuring a unusually wide line of darker fine debris flow.

Sound principles of super-positioning seem to indicate Armstrong is an old crater on the main-sequence of lunar crater types, barely large enough to have once supported a floor, now long buried by steady mass wasting. It's a pounded, rounded and well-gardened interior and has none of the great boulders on the rim that would set it apart as relatively young. Still, the interplay of epochs that have etched their passing on the Tranquillitatis basin (if it is a true impact basin) is at least as delightful as clouds in a spring day sky. LROC NAC M126765005L [NASA/GSFC/Arizona State University].

Without the jagged features characteristic of younger similarly-sized craters, craters like South Ray, not yet baked evenly into reddened optical maturity, even the highest resolution segment of the mosaic doesn't invite anyone to go through a similar time-consuming process of creating a wall-sized picture of Armstrong crater. Flight planners did not choose this place on the Moon for its drama.

Site B was selected for the first landing so that first pilot would not have to take control from an over-loaded on-board computer to dodge boulders looming up from the spot where the delicate Lunar Module was trying to land.

The dark-line and notch at "5 o'clock" on the rim of Armstrong (inset at original resolution) is more than a superficial darker debris flow, after all. The relief at angles of illumination unavailable at high-resolution definitely show a notch in the crater rim anatomy, at 60 meters resolution. There is also a stream of secondary cratering that amounts to a ray, perhaps from Theophilus. The white arrow is the landing site of Apollo 11. LROC Wide Angle Camera mosaic (604nm) from several orbital passes July 2011 [NASA/GSFC/Arizona State University].
Fortunately, the relatively small crater is not terribly difficult to spot using a modest telescope, if, in addition, an Earth-bound observer has more than a passing knowledge of the Moon's nearside in general and the Sea of Tranquility in particular.

Bit by slow bit we are gathering information that adds up to a fairly accurate simulation of the Moon, but to experience a truly accurate picture of our own back yard we are also having confirmed what we already knew.
You really have to have been there.

From a 33 percent reduction of a truly spectacular color mosaic of the Moon captured by the "miracle boys of Minsk," Astronominsk, April 6, 2009.

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