View Full Version : Lunar Dust Transport Still a Mystery

2010-Dec-15, 08:40 PM
There are times when Moon appears to have a tenuous atmosphere of moving dust particles that are leaping up from and falling back to the Moon’s surface. First seen during the Surveyor and Apollo eras, these observations were completely unexpected, and scientists today are still trying to understand this phenomenon. The first indication that something [...]

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2010-Dec-19, 01:25 AM
The observations recorded in the Apollo 17 orbital sketches seem to primarily record the outer corona and inner zodiacal light. The latter is what appears in the photographs taken from Lunar orbit, the streamers are faint and low contrast, and can be visually observed better than they could be readily photographed.
Such coronal streamers extend to distances consistent with the Lunar orbital observations, and are regularly photographed by spacecraft such as SOHO. The LASCO C3 images show such detail in its extant and variability:


An excellent composite image of the inner and outer coronal details by Fred Espenak can be seen here:


The outer corona and inner zodiacal light is thus being recorded, in observations which demonstrate the abilities of human vision to detect subtle and faint detail.

The 'Lunar horizon glow' is an interesting problem in detection and explaining.

A nice visual summary of the subject is McCoy's 'Photometric studies of light scattering above the lunar terminator':


The Surveyor V corona image included therein seem to show some ray and spike structure. Surveyors 6 and 7 seem to record a smoother inner corona, at least within the limitations of the television camera used. The horizon 'rim lighting' is at the far horizon, closely adhering to the most distant surface relief. This suggests a surface effect or perhaps a closely 'ground hugging' source of the forward scattered light. I suggest that a superficial sprinkling of glassy dust is giving us a forward scattered 'peek' at the directly unseen brighter inner corona, and finally the sun itself, just as one can see bright outlines behind dusty surfaces, mountains, etc when the Sun is just hidden behind them. I recall reading of this idea long ago.
The referenced PDF also shows tracings of brightness contours on photographs taken of the inner zodiacal light in Lunar orbit. They don't seem to confirm a horizon hugging brightness distribution as is shown in the sketches. Even in an image showing the Earth lit horizon, the faintest observable contours of the portion of recorded part of the the inner zodiacal light seem to show no obvious trend toward spreading out along the horizon. Modern scans and studies of the original film should be done to see what might be mined from the data.
So what is one to make of the including of a 'horizon glow' in the sketches based on visual observations? The characteristics of Human vision are the key to what is recorded visually as opposed to film. As time passed in the corona observations the astronauts eyes were steadily dark adapted, allowing the outer streamer details to be seen. The Zodiacal glow extended further than the brightness contour selected indicates, petering out gradually to the surrounding blackness of space. The dark Lunar horizon provided a sharp contrast boundary much easier to visually detect than a very gradual one spread out some tens of degrees. I suspect if ideal conditions could be arranged the fainter glow recorded along the horizon would reveal brightness contours tending to outline the shape of the sketched one, conforming to the widely observed Zodiacal light.

Don Davis

2010-Dec-20, 02:30 AM
I wasn't even halfway through the article when the old trick of sticking balloons to the wall via friction induced charging came to mind. Where this becomes pertinent is when said balloon finally releases from the wall. The balloon doesn't simply fall, it's pushed away from the wall, sometimes up to four or five inchs before gravity pulls it down. It stuck because its charge was opposite that of the wall, and when it finally matchs the balloon is repelled for having the same charge.