On Wed, 25 Jun 2008 15:05:19 -0400, alexy wrote:

wrote:



Well, you directed the question to flight simmers and trolls. If you
want to open it up to non-pilot lurkers, I'll take a guess. Assuming
you will reveal the correct answer and explain it.

glory be, what can the answer be?


My guess is that since the plane will subtend a much smaller angle
than the sun, there would be no noticeable shadow. My guess is a
"halo" around where the shadow would be, caused by diffraction, Since
most of the edges tend to be inline with the plane's axis or
perpendicular to it, it seems that this halo might be somewhat
brighter on those two axes, but I wonder if that would be noticeable.
The halo might have a slightly bluish cast, since the red end of the
spectrum would get diffracted more, and being over a larger area would
be not as bright.

So, what's the real answer?


sitting on the ground with the sun about 93 million miles away the
aircraft casts a sharp shadow on the ground.

at 500ft altitude the aircraft is 500ft closer to the sun than the
previous 93 million miles, which is next to no change at all, so there
will be very little change to the shadow you'd think. but there is. at
500ft the aircraft shadow is a very indistinct blur surrounded by a
halo of bright light.

at 4,500ft (the original question) the aircraft has no shadow at all
but at the sub solar point (were you'd think the shadow should be)
there is a distinct bright area tracking along under the aircraft.

for thirty years this quietly puzzled me. it is a fact that aircraft
at altitude have no shadow. below them tracking along the ground is a
bright spot of light.

the reference I gave gives details of some original work by Fresnel
which proposed that light passing beside a gravitational mass should
be bent slightly by the mass and behind the body there should be a
bright spot. this seems to me to be the explanation for the absense of
the shadow. the mass of the aircraft acts as a gravitational lens and
this causes the bright spot.

the reason I asked the question was to point out that simulators work
on a simplified model of the reality that real pilots are exposed to.
people like mxsmanic seem utterly oblivious to the fact that their
exposure to the simulator will never give them competent knowledge
because all they are exposed to is a simplified model of reality. it
is only exposure to the actual reality that will allow you to achieve
competent knowledge.

if simulators dont get something as simple as the aircraft's shadow
right can you trust that anything else they show you is right?

Stealth Pilot