1. A lithographic apparatus, comprising: an illumination system that conditions a beam of radiation; an array of individually controllable elements that pattern the beam; a beam divider that divides an intensity of the patterned beam into at least first and second fractions, each having substantially a complete cross-section of the pattern; a projection system that projects the first fraction of the patterned beam onto a target portion of a substrate; an image sensor that inspects at least a portion of the cross-section of the second fraction of the patterned beam; and an actuator that moves the image sensor to select the portion of the cross-section of the second fraction of the patterned beam that is inspected