READING 'SIGN'

Information can be encoded in different ways, and writing it down in words is only the most common method. Drawings, dances, music, and other media are other ways that humans spread information. Nature has its own schemes, from DNA/RNA to hormonal indicators to shapes, motions, and physical traces of objects both living and non-living.

A 1990 movie about a Khoisan bushman who could expertly 'read' the land and the physical environment [sound, smell, light/shadow, flows of wind and water, etc] made that profound point sweetly and subtly when he is depicted as he realizes that a stranger he was trying to rescue saw everything he showed her, but had no idea what any of it meant. She was, in terms of his own universe, illiterate.

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Just as with….

 Plumes have different manifestations depending on....






  

The most basic parameter that an ascent rocket plume can provide  perceptive observer is its altitude, because of one spectacular change in appearance at a known altitude range. As the rocket climbs out of the atmosphere, the air density thins rapidly. After a short while it is too thin to support winged [or buoyant] craft, and soon thin enough not to destroy objects traveling through it at near-orbital [or higher] speeds. This transition occurs between 80 and 100 kilometers [50 and 65 miles] approximately. It is called the Karman boundary, or sometimes -- if  precise number is needed] the Karman Line. Just for picking even numbers, Europeans like '100 km', while US Air Force rocket planes [and NASA's X-15] specified 50 miles. 

A rocket plume's shape changes dramatically at this boundary. In lower, thicker air, the plume is constrained and suspended in air, broadening only slowly, while also being quickly kinked by high-altitude crosswinds.  But as the rocket enters the Karman boundary the plume widens dramatically, and the plume particles are no longer stopped [and then supported] by air molecules -- instead, they fly out of the engine on unconstrained ballistic paths, creating a wide fan-like structure which rapidly collapses as the particles spread and then fall into the upper atmosphere where they disperse. The lower sub-Karman trail can linger for an hour or so,    

   

staging

     


Because the most spectacular plumes are at twilight, there is an additional clue to read...

  

The next important parameter that a rocket plume's appearance provides is absolute size.