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