Derivations of this phenomenon may assume that objects satisfy the “singular isothermal sphere” profile. The KSB method is used to combat the PSF uncertainty produced in this phenomenon. The background distribution of dark matter can be found by averaging the orientations of galaxies due to the shear produced by this phenomenon. The observation of the “Twin Quasar” confirmed Fritz Zwicky’s prediction of this phenomenon. The quantity [read slowly] “four times big G times mass (-5[1])over radius times c-squared” equals this phenomenon’s angle of deflection. When a source, observer, and intermediary are all aligned, this phenomenon can produce a “halo effect” called (10[1])Einstein rings. For 10 points, name this phenomenon in which astronomical bodies bend the path of (10[1])light. ■END■