Interesting optical effect

[Robert Lyons]

On a commercial flight recently, I saw a fascinating optical effect.
I believe I understand what I saw, but would appreciate confirmation
from experienced flyers out there.

We were at cruising altitude, mid-trip. The air was clear, except
for a thin haze layer below us, perhaps midway between the aircraft
and the ground. Visible in that haze was an image of the sun, cast
presumably by tiny lakes below us. Larger lakes didn't work - the
cast reflection would get too large and out-of-focus.

You all probably know about using pinhole viewers to see an eclipse.
You may also know that you can view an eclipse with a fragment of a
mirror, if it is small enough (or if you cover up most of a larger
mirror, leaving a small hole). It will project a perfect image of
the eclipsed sun on a convenient wall or floor. I'm pretty sure this
is what I was seeing from the air, projected on that flat haze layer.

My questions:

1) Has anyone else seen this effect? Is it well-known?

2) (the real question) has anyone seen it during an eclipse? Can you
confirm that it gives you an eclipsed image?

- Bo

[Maule Driver]

"Robert Lyons" > >
> You all probably know about using pinhole viewers to see an eclipse.
> You may also know that you can view an eclipse with a fragment of a
> mirror, if it is small enough (or if you cover up most of a larger
> mirror, leaving a small hole). It will project a perfect image of
> the eclipsed sun on a convenient wall or floor. I'm pretty sure this
> is what I was seeing from the air, projected on that flat haze layer.
>
A cute pinhole eclipse image I've seen was in a conference room with thin
slat blinds covering the windows. Every slat had two or more little holes
for string or something. Every holes shadow projected on the floor showed a
perfect little eclipse. There many dozens of them.

[Robert Lyons]

Maule Driver wrote:

> "Robert Lyons" > >
>
>>You all probably know about using pinhole viewers to see an eclipse.
>>You may also know that you can view an eclipse with a fragment of a
>>mirror, if it is small enough (or if you cover up most of a larger
>>mirror, leaving a small hole). It will project a perfect image of
>>the eclipsed sun on a convenient wall or floor. I'm pretty sure this
>>is what I was seeing from the air, projected on that flat haze layer.
>>
>
> A cute pinhole eclipse image I've seen was in a conference room with thin
> slat blinds covering the windows. Every slat had two or more little holes
> for string or something. Every holes shadow projected on the floor showed a
> perfect little eclipse. There many dozens of them.
>
>


Yup - I've seen a similar effect with sunlight coming through
the canopy of a tree. Thousands of little eclipse images. The
holes have to be quite small relative to the size of the cast
image, in order to keep the projection in focus.

The in-the-air version I saw was similar, in that it didn't
work if we were passing over a larger lake. If the lake was
large enough for me to see it clearly, it was too big, and the
resulting image was distorted and out-of-focus. The lakes
that worked the best were barely visible to me - the tiniest
pinpricks of reflected light. That's what convinced me that I
was interpreting the phenomenon correctly.

- Bo

[G.R. Patterson III]

Robert Lyons wrote:
>
> We were at cruising altitude, mid-trip. The air was clear, except
> for a thin haze layer below us, perhaps midway between the aircraft
> and the ground. Visible in that haze was an image of the sun, cast
> presumably by tiny lakes below us. Larger lakes didn't work - the
> cast reflection would get too large and out-of-focus.

Sounds similar to an effect called "sun dogs". I've only seen it once, and then
only from the ground.

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

[Kobra]

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

"Robert Lyons" > wrote in message
...
> On a commercial flight recently, I saw a fascinating optical effect.
> I believe I understand what I saw, but would appreciate confirmation
> from experienced flyers out there.
>
> We were at cruising altitude, mid-trip. The air was clear, except
> for a thin haze layer below us, perhaps midway between the aircraft
> and the ground. Visible in that haze was an image of the sun, cast
> presumably by tiny lakes below us. Larger lakes didn't work - the
> cast reflection would get too large and out-of-focus.
>
> You all probably know about using pinhole viewers to see an eclipse.
> You may also know that you can view an eclipse with a fragment of a
> mirror, if it is small enough (or if you cover up most of a larger
> mirror, leaving a small hole). It will project a perfect image of
> the eclipsed sun on a convenient wall or floor. I'm pretty sure this
> is what I was seeing from the air, projected on that flat haze layer.
>
> My questions:
>
> 1) Has anyone else seen this effect? Is it well-known?
>
> 2) (the real question) has anyone seen it during an eclipse? Can you
> confirm that it gives you an eclipsed image?
>
> - Bo
>

[Peter Duniho]

"Kobra" > wrote in message
...
> 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.

All rainbows are circular. It just happens that when you are standing on
flat ground, you can't see the whole rainbow.

Since the center of any rainbow (all of which are circular) is a point on a
line projected from the light source through the viewer, the shadow of the
viewer (an airplane in your case) will always be smack in the center of the
rainbow, even if the viewer is moving.

For more sunlight effects, just look at your shadow on the ground at any
time during the day. Depending on the time of day and where your shadow is,
you'll see a variety of effects. My two favorite ones are the bright spot
with the shadow in the middle that you see on forested areas (due to the way
the trees reflect the sunlight, the reflection is brightest where the sun is
directly behind the viewer), and the moving blob of red you see when your
shadow is passing over a large parking lot (the taillight reflectors reflect
the sunlight back to you very brightly).

> 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.

If you saw that, I'd suggest you were flying too low. :)

Seriously though, the effect described by the link you provided appears to
be specifically restricted to human shadows atop a shadow of terrain
(usually a peak), along with a rainbow. I wouldn't use the term they are
using to describe the similar thing viewed from aloft in an airplane.

Pete

[Maule Driver]

Two weeks ago (Friday) we flew from NC to Saratoga Springs. My co-pilot
kept talking about the colors in the clouds. It was a sparkling CAVU day at
7500 feet over NJ and NY. I was too busy looking out the other side
reliving past flights.

I explained that the clouds below us were reflecting the fall colors on the
ground. She insisted that it wasn't that and wen I looked, we had rainbow
circles on each cloud as we passed. Quite beautiful. A fantastic day to
fly.

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.

"Kobra" > wrote in message
...
> 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
>
> "Robert Lyons" > wrote in message
> ...
> > On a commercial flight recently, I saw a fascinating optical effect.
> > I believe I understand what I saw, but would appreciate confirmation
> > from experienced flyers out there.
> >
> > We were at cruising altitude, mid-trip. The air was clear, except
> > for a thin haze layer below us, perhaps midway between the aircraft
> > and the ground. Visible in that haze was an image of the sun, cast
> > presumably by tiny lakes below us. Larger lakes didn't work - the
> > cast reflection would get too large and out-of-focus.
> >
> > You all probably know about using pinhole viewers to see an eclipse.
> > You may also know that you can view an eclipse with a fragment of a
> > mirror, if it is small enough (or if you cover up most of a larger
> > mirror, leaving a small hole). It will project a perfect image of
> > the eclipsed sun on a convenient wall or floor. I'm pretty sure this
> > is what I was seeing from the air, projected on that flat haze layer.
> >
> > My questions:
> >
> > 1) Has anyone else seen this effect? Is it well-known?
> >
> > 2) (the real question) has anyone seen it during an eclipse? Can you
> > confirm that it gives you an eclipsed image?
> >
> > - Bo
> >
>
>

[Peter Duniho]

"Maule Driver" > wrote in message
. com...
> 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.

See my other post. That "bright spot" is simply your position relative to a
reflective surface. Your plane isn't projecting it. That just happens to
be the spot where the sunlight is reflected by the greatest amount.

Note that "reflective surface" doesn't have to be man-made. Trees, grass,
shrubs, snow, sand, etc. are all reflective to some degree (just as you are
reflective :) ).

Pete

[Jay Beckman]

"Kobra" > wrote in message
...
> 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

FWIW...

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

[Teacherjh]

>>
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.

Jose

--
(for Email, make the obvious changes in my address)

[G.R. Patterson III]

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.

[JamesB]

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

[Robert Lyons]

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

[C J Campbell]

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.

[C J Campbell]

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.

[Maule Driver]

"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.

[Maule Driver]

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.

[Mark Mallory]

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.

[Peter Duniho]

"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