Bruce Hoult wrote:

It's amazing how hard it is to get *true* no-visual-reference conditions
in IMC.

I've done some flying with a commercial pilot friend doing night freight
runs in small turboprops. Even in the clouds in the middle of nowhere
in NZ you can almost always see some speck of light out of the corner of
your eye, whether a farmhouse or a star, and that gives you roll
information even when you're not looking at the AH. You don't realize
how much this helps until the first time there really *is* nothing out
there.

There have been an amazing number of Navy pilots that have flown into
the water as they mistaked boat lights for either stars or an aircraft
they were joining on. I know, not pertinent to gliders, but the optical
illusions of sort of IMC/VMC can be intense and almost more disorienting.