The Beta Angle is the signed angle of the apparent vector to a central body, relative to the orbital plane. The signed angle is positive when the apparent vector is in the direction of the orbit normal. The orbit normal (which is normal to the orbital plane) is parallel to the orbital angular momentum vector, which is defined as the cross-product of the inertial position and velocity vectors. The light time delay is actually computed between the central body used to compute the beta angle and the vehicle's central body, rather than directly from the object itself.