Spatial orientation of an example blazar–neutrino pair. The blazar is shown as a purple star. The most likely arrival direction of the neutrino is shown by the orange cross. The ≳90%-likelihood error region of the neutrino (see Sect. 2.1) is shown by the green ellipsoid. d_BN, ϕ is the distance between the blazar and the center of the neutrino error ellipsoid, shown by the dotted purple line. R_ϕ is the distance between the edge and center of the ellipsoid along the line that goes through the blazar, shown by the black double-headed arrow oriented at a ϕ angle from the northern axis. α^+/− and δ^+/− represent the asymmetric 2σ Gaussian error bars in RA and Dec, respectively.