Interesting optical effect

Teacherjh wrote:


If you want to bounce a target from directly out of the sun, place the
sunball squarely on your intended target.


I know what each of these words means, but when put together in this manner I
can't make head or tail out of it.

Translation - If you're flying a fighter and wish to attack another aircraft
while keeping the sun directly behind you so he can't see you, then maneuver
your plane until that sunball hits his plane and dive straight at him.

George Patterson
If you're not part of the solution, you can make a lot of money prolonging
the problem.

Kobra wrote:

This may be something different, but I saw this flying to Lake George two
weeks ago. I was about 1000' above the deck with the Sun high above me. My
frontseat passenger keep saying a circular rainbow was following us and that
the plane's shadow was in the middle of it. She took a picture of it that I
thought would never show up. But it did. I have to get her to scan it.

I told a friend of mine about it and he said that effect has a name. He
found it on the web and sent me this link:

http://www.touchingthelight.co.uk/features/brocken.htm

Low and behold...that is what we saw.

Kobra


See the book "Chasing the Glory" by Michael Parfit. A very good read by
a
small plane pilot flying around the US. The 'Glory' is that which you
saw on the cloud/haze layer.

JamesB

To email me get the lead out

Maule Driver wrote:

Now, who can explain the bright spot that our plane projects down sun? It's
like a giant headlight and is particularly noticeable late in the day with
the sun behind.

You may be describing the effect I saw, or you may be describing the effect
that Peter Duniho already told you about: the point of highest reflectivity
of the clouds.

The difference is whether the image is an in-focus view of the sun (it'll be
exactly the same apparent size as the sun, too) or whether it's a diffuse
zone of brightness with no particular focus.

The optical effect I'm asking about would be the in-focus sun image, and
could not be seen when the deck is relatively solid, as it depends on light
reflecting from a lake (i.e. on the *ground*, where most well-behaved lakes
are found) and projecting onto a thin haze-layer. It probably also requires
an inversion or some other mechanism of making a boundary to hold the thin
haze layer.

The effect Peter is describing (if I understand correctly) should be very
common, basically visible whenever you are flying over the deck. It's the
light of the sun, back-scattering off the clouds. The ground needn't be at all
visible (better if it's not, in fact) and the 'glow' will be diffuse and un-
focused.

Now, you say it's "like a giant headlight" ... in focus, or not?

- Bo

Last night I was flying about sunset and the sun cast a perfect reflection
of itself on a thin cloud just above it on the horizon. We had two suns to
look at for about half an hour.

The rainbow is a perfect circle centered around the observer. The rainbow
that you see will be slightly different from a rainbow seen by a person
standing right next to you. If you move, the rainbow will always move with
you. The shadow of the observer is always in the exact center of the
rainbow.

"Robert Lyons"
The effect Peter is describing (if I understand correctly) should be very
common, basically visible whenever you are flying over the deck. It's the
light of the sun, back-scattering off the clouds. The ground needn't be at
all
visible (better if it's not, in fact) and the 'glow' will be diffuse and
un-
focused.

Actually I see it on the ground but it is diffuse and unfocused - like a
very strong headlight shining on a very distant area. You just get a
diffuse bright spot.

I think I get Peter's concept and understand it but can't quite get it to
'intuit'. But makes some sense. Can't quite understand why the area on the
ground where sunlight would reflect back at 180deg (or normal to the average
surface) would be so much brighter than points where the sunlight would
reflect back at say 45 deg to the avg surface. Doesn't make sense when I
think of a forest of trees, but it is quite clear when same light refects of
a truck on a highway. So I kind of get it. Thanks Peter and Robert.

That makes sense!
"G.R. Patterson III"
Translation - If you're flying a fighter and wish to attack another
aircraft
while keeping the sun directly behind you so he can't see you, then
maneuver
your plane until that sunball hits his plane and dive straight at him.

Maule Driver wrote:

Actually I see it on the ground but it is diffuse and unfocused - like a
very strong headlight shining on a very distant area. You just get a
diffuse bright spot.

I think I get Peter's concept and understand it but can't quite get it to
'intuit'. But makes some sense. Can't quite understand why the area on the
ground where sunlight would reflect back at 180deg (or normal to the average
surface) would be so much brighter than points where the sunlight would
reflect back at say 45 deg to the avg surface. Doesn't make sense when I
think of a forest of trees, but it is quite clear when same light refects of
a truck on a highway. So I kind of get it. Thanks Peter and Robert.

Peter didn't really explain it. Except for specially-designed surfaces that
incorporate corner reflectors (like taillights, or bicycle reflectors), a
randomly-oriented surface doesn't preferentially reflect light back in the
direction of it's source. However, the effect has a very simple explanation:

The bright spot is simply the result of the absence of SHADOWS cast by objects
on the ground. On a sunny day, EVERY object on the ground - rocks, blades of
grass, trees, people - casts a SHADOW. When one looks at the ground from a
considerable distance, each tiny object and it's *shadow* are all averaged
together to contribute to the total brightness of the surface. However, when
one looks at the ground from the direction of the Sun, every shadow DISAPPEARS
behind the object that casts it! As a result, in that ONE direction there are
NO SHADOWS to dilute the intensity of the light reflected back to the observer;
the result is a *bright spot* in which the apparent reflectance is very nearly
DOUBLE that in any other direction.

The effect is not noticed if you are standing on the ground (or very near the
ground in an airplane) because your OWN shadow blocks the sunlight in that
direction. When the airplane climbs to a considerable height (such that it
appears much smaller than the Sun as seen from the ground) the shadow of the
airplane ceases to exist and no longer blocks the light in the "anti-sun"
direction, allowing the effect to be seen.

"Mark Mallory" wrote in message
...
Peter didn't really explain it.

I wrote:

"Your plane isn't projecting it. That just happens to be the spot where the
sunlight is reflected by the greatest amount."

Are you saying that you disagree that the sunlight is reflected back to the
viewer by the greatest amount?

Your post certainly seems to agree with mine. Yet, you seem to be taking
issue with it, for some reason.

Pete