  Given a (d+1)-dimensional spacetime (M,g), one can consider the set N of all
its null geodesics. If (M,g) is globally hyperbolic then this set is naturally
a smooth (2d-1)-manifold. The sky of an event x in M is the set X of all null
geodesics through x, and is an embedded submanifold of N diffeomorphic to
S^{d-1}. Low conjectured that if d=2 then x,y are causally related in M iff X,Y
are linked in N. We prove Low's conjecture for a (large) class of static
spacetimes.
