FreeLists / az-observing / [AZ-Observing] Thermal Brightening from the Impactor?

["Stanley A. Gorodenski" <stan_gorodenski@xxxxxxxxxxxxx>]

Today in S&T I read the following:

"The following was posted by Jeff Schroeder at Wrightwood:
Two minutes after the predicted impact time, I saw a faint unstructured 
spot appear that was about 10 to 15 arcseconds wide."

In a previous email message to Az-Observing before the impact event I 
assumed that what we would see visually is reflected sunlight off the 
ejecta. In that message I assumed the ejecta travels the same speed as 
the Impactor, i.e., 6.3 miles per second. I calculated that in 30 
minutes the ejecta would subtend an arc angle of 0.47 arc minutes or 
about 28 arc seconds, and that this probably would be able to be 
observed visually from Earth.

However, if Jeff Scroeder actually observed a spot at least 10 arc 
seconds wide, this would mean the ejecta was traveling at a minimum of 
33.5 miles per second, or over 5 times the speed of the ejecta. If 
Jeff's observations are accurate with respect to size, and if it is not 
possible for ejecta to travel this much faster than the speed of an 
impactor (be it _the_ Impactor or a chunk of rock), than this says that 
the impact caused an intense thermal light flash that was diffused by 
the coma surrounding the nucleus into a much larger area then the actual 
ejecta. If this is a valid explanation, then what Jeff observed was this 
diffused glow, and not the actual ejecta. Any thoughts on this?
Stan




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