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

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

Opps. When I said "or over 5 times the speed of the ejecta" I meant to 
say the Impactor not ejecta.


Stanley A. Gorodenski wrote:

>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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