Yerkes director Kyle Cudworth points to two stars (HIP 106074, left, and SAO 107179) that had moved between the years 1916 and 1997. Cudworth stacked two plates on top of one another, centered on the object M-15, to demonstrate the changes seen with the Yerkes 40 inch refrector over that epoch. The original photo was taken by E. E. Barnard, a pioneer in astrophotography. His original exposure was three hours.