Electromagnetic waves can have handedness associated with their polarization. Polarization of an electromagnetic wave is the property that describes the orientation, i.e., the time-varying direction and amplitude, of the electric field vector. For example, the electric field vectors of left-handed or right-handed circularly polarized waves form helices of opposite handedness in space as illustrated by the adjacent animation. Polarizations are described in terms of the figures traced by the electric field vector as a function of time at a fixed position in space. In general, polarization is elliptical and is traced in a clockwise or counterclockwise sense. If, however, the major and minor axes of the ellipse are equal, then the polarization is said to be circular . If the minor axis of the ellipse is zero, the polarization is said to be linear. Rotation of the electric vector in a clockwise sense is designated right-hand polarization, and rotation in a counterclockwise sense is designated left-hand polarization. When deciding whether the rotation is clockwise or counterclockwise, a convention is needed. Optical physicists tend to determine handedness from the perspective of an observer looking towards the source from within the wave, like an astronomer looking at a star. Engineers tend to determine handedness looking along the wave from behind the source, like an engineer standing behind a radiating antenna. Both conventions yield opposite definitions of left-handed and right-handed polarizations and therefore care must be taken to understand which convention is being followed.