The broadened shapes of absorption lines in the optical spectrum depend on v rot sin(i), where i is the angle between the line of sight and the rotation axis, permitting the study of the rotational velocity's line-of-sight component v rot. This is calculated from Fourier transforms of the line shapes, using equation (2) below for v rot at the equator and poles. See also plot 2. Solar differential rotation is also seen in magnetograms, images showing the strength and location of solar magnetic fields.