Parallax is the scientific term for relative displacement of objects
observed at different distances. Parallax is used often by astronomers to
ascertain the distance of objects within our own solar system, and even
nearby stars by observing them from different points in the earth's orbit
around the sun.

I the case of the turn coordinator, the reason the ball appears off center
when observed from the side is due to parallax. This does not mean that
this is the only instance in which the concept of parallax is applied. The
original poster described another circumstance that results from parallax;
i.e. a moving object appearing to be stationary when compared to the
background when the observer is also moving at a rate and in a direction
that allows the parallax to create the illusion that the airplane is
stationary when in fact it is not...

I just wanted to point out to the group that this is a well known phenomenon
that has a scientific term to describe it.

Dean Wilkinson

"Robert M. Gary" wrote in message
om...
"Dean Wilkinson" wrote in message
...
Its called parallax. Your motion, the motion of the plane, and the
background were in the right configuration so that the parallax made the
plane appear to be stationary when in fact it was not...

Are you sure? Parallax is when you try to show a student how to make a
coordinated turn and you end up with the ball out to the left because
you aren't looking at the turn coordinator straight on.

-Robert, CFI