In particular, consider a pair of Rindler observers with coordinates x = x 0 , y = 0 , z = 0 and x = x 0 + h , y = 0 , z = 0 respectively. (Note that the first of these, the trailing observer, is accelerating a bit harder, in order to keep up with the leading observer). Setting d y = d z = 0 in the Rindler line element, we readily obtain the equation of null geodesics moving in the direction of acceleration: