The Largest Star?

Close to the brilliant star Capella, in the constellation of Auriga, there is a particularly interesting star, Epsilon Aurigae. We know it is made up of two stars, but we can only see one directly. The mysterious companion is invisible, but can be detected by infra-red. It may be the largest star known to science-or, just possibly, it might be what is known as a 'black hole'. This summer the companion is due to pass in front of the visible star, so that astronomers will be doing all they can to find out just what it really is. Patrick Moore talks to Heather Couper who has made a special study ef this strange object.