Re: Mystery tracks through M42
Sat, 9 Oct 1999 01:59:36 EDT

Hello again
     I still think they all could be aircraft.  As Robert Matson points out:

> Also note the difference in color:  the
>E-W tracks are white/gray; the N-S ones are reddish.
>So, I think we're talking about something atmospheric.  The
>angular separation is about 0.05 degrees.  If the date and
>time reported are correct, then M42 was about 40 degrees
>above the horizon at the start of the picture, and 34 degrees
>by the end. 

     A Southbound aircraft's position lights would appear reddish since the 
position light on the left side of an aircraft is red.  It's green on the 
right and white on the tail.  Depending on the observers position relative to 
the aircraft, a combination of colors may be seen.  If you consider a top 
view of an aircraft, green should be visible to observers positioned anywhere 
from the nose, clockwise to 110 degrees where they should then see white for 
the next 140 degrees, and then red for the last 70 degrees.  Required 
visibility (+/- horizontal) depends on the certification date of the aircraft 
and may be as small as (+/-) 30 degrees.  An aircraft might also only have a 
single strobe on the top of it's tail which could be obscured by the wing 
planform or empennage depending on the observers aspect and distance.  In a 
similar manner, position/strobe lights may be blocked by engine nacelles.  A 
white color is consistent with the tail aspect of a Westbound aircraft.
     I noticed some gross buffonery on my part in a previous post.  I 
incorrectly computed the horizontal ranges given aircraft at various 
altitudes (only about half of what they should have been).  These have been 
corrected and updated using 37 degrees elevation as a midpoint and are 
graphically depicted on an aeronautical charts showing the photographers 
relative position to various airways and other subdivisions of airspace.  Of 
particular significance is Instrument Route 012 (IR-012) which is directly 
over the photographers location.  This route is flown by C-17's from 
Charleston AFB, SC at altitudes from 300' AGL to 4000' MSL.  The bright green 
lines represents the centerline and the red lines describe the corridor of 
the route (5 nm either side of center).  An aircraft can legally fly anywhere 
within the corridor while on the route.  Although I am unfamiliar with the 
exact intensities or spatial position of the exterior lighting on a C-17, it 
may be possible that a single aircraft's lights described the 4 arcs on the 
photograph.  The aircraft would be within the FOV for less than 2 seconds 
anywhere within the corridor at the speeds flown.  While possible, that does 
not explain the absence of *required* white lights.  
     In either case, it is interesting to look at these images located at:
airways.jpg - shows the airways and airspace around the photographer
ir012.jpg - shows IR-012's relationship to the photographer
kellync.jpg - 1:50,000 chart of the photographs origin

Shawn Fleming
32 34.127 / -93 39.034 / WGS-84
61.9 meters

Unsubscribe from SeeSat-L by sending a message with 'unsubscribe'
in the SUBJECT to