  Laboratory-based optical analogs of astronomical objects such as black holes
rely on the creation of light with an extremely low or even vanishing group
velocity (slow light). These brief notes represent a pedagogical attempt
towards elucidating this extraordinary form of light. This paper is a
contribution to the book Artificial Black Holes edited by Mario Novello, Matt
Visser and Grigori Volovik. The paper is intended as a primer, an introduction
to the subject for non-experts, not as a detailed literature review.
