Icebergs and Crouching Giants

How many star systems or galaxies are there? It now seems that there are many more than has been believed - some of them so dim that they are barely visible, so that we are seeing only 'the tip of the iceberg'; others so compact, like crouching giants, that they have been mistaken for stars. Professor Michael Disney of Cardiff University, who has been deeply involved in this new research, joins Patrick Moore to give the latest results.