Cosmos — Episode 4: A Sky Full of Ghosts

You are watching the episode A Sky Full of Ghosts An exploration of how light, time and gravity combine to distort our perceptions of the universe. We eavesdrop on a series of walks along a beach on summer nights in the year 1809. William Herschel, whose many discoveries include the insight that telescopes are time machines, tells bedtime stories to his young son, John, who will grow up to make some rather profound discoveries of his own.