"Paul Schlyter" writes:

The Black Drop is an effect of how our eyes perceive when two unsharp
edges between bright and dark approach one another. It can be readily
simulated by keeping two of your fingers as close to your eye as you
can
and then let the fingers approach one another: they seem to touch
before
they actually touch.

They gave this example on NASA TV also, but it is a bit misleading
because the fingers effect is caused by diffraction (wave bending as a
sharp edge intervenes), whereas the black drop effect is caused by
variable refraction from moving air cells in Earth's atmosphere. Light
in space is not spread in this way, as is evident from photoelectric
observations of lunar occultations, which show the star disappearing in
milliseconds rather than seconds. (That effect really is caused by
diffraction.) -|Tom|-


Tom Van Flandern - Washington, DC - see our web site on replacement
astronomy research at http://metaresearch.org