A sphere, moving at various speeds to the right, is observed from three diameters distance from its nearest point on the surface. The left image shows the sphere's measured, Lorentz-contracted shape. The right image shows the visual appearance of the sphere. The red cross marks the point closest to the eye. The sphere maintains its circular outline since, as the sphere moves to the right, light from further points of the Lorentz-contracted ellipsoid takes longer to reach the eye. The circularity preservation comes from the fact that the transformation from one observer's "visual sphere" to that of another observer is a conformal map. The general proof of the conformality may be found in "Spinors and Spacetime", by Penrose and Rindler.