Description
If a black hole is seen against a backdrop of light sources, it shows a black disc known as the ``shadow'' of the black hole. In the first part of the talk I recall how the boundary curve of the shadow can be analytically calculated for an isolated (Schwarzschild or Kerr) black hole. Then I discuss how the cosmic expansion, in the simplest case just driven by a
cosmological constant, would influence the size of the shadow and if this influence could be of any relevance for actual observations of black-hole shadows.
