Publication date: Sep 1990
The static region of the Schwarzschild-de Sitter spacetime is studied
from the point of view of the optical reference geometry introduced by
Abramowicz et al. (1988). It is shown that, in this geometry, the
geodesic curvature of circles r = const is independent of the parameter
Lambda (cosmological constant) of the spacetime. The consequence of this
fact for circular photon orbits is discussed.