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One important consideration for visual binary orbitals is that the plane of orbital revolution for such systems is not usually perpendicular to our line of sight. In general, there is some tilt angle i, as illustrated in the adjacent figure.
Thus, when we see the orbit of a visual binary we do not see the actual orbit but only the projection of that orbit on the celestial sphere. For example, if the orbit looks like an ellipse, that could be because the orbit actually is elliptical, or because the true orbit is a circle but we are seeing it from an angle that makes the circle look flattened and therefore elliptical. In some cases it is possible to determine the angle i by careful measurement in order to deduce the true orbits of the binary system. In other cases we cannot and the angle i remains uncertain.