Documentary examining the popularity of the reality TV star who conquered controversy to become one of the most popular celebrities in British pop culture. The programme charts her rise to fame with Girls Aloud, and her success on The X Factor and the end of her marriage to Chelsea football player Ashley Cole. Includes contributions by Cheryl's friends and colleagues

In Power, Professor Robert Bartlett lays bare the brutal framework of the medieval class system. Inequality was as part of the natural order, the life of serfs little better than those of animals, the knight’s code of chivalry more one of caste solidarity than morality. The class you were born into determined who you were. There were three classes, or estates: those who pray (the clergy), those who fight (the aristocratic warrior class of knights) and those who work (everybody else – in practice, usually serfs on a knight’s estate).

The MiG 15 was one of the 20th century’s most feared high-performance weapons. When it first appeared in 1950, its high speed, lightning maneuverability, and intense firepower outclassed everything in the sky. During the Korean War, when Soviet MiGs engaged with America’s F 86 Sabre jets, they finally met their match and a new era in air warfare had begun. Features exclusive interviews with MiG fighter pilots who flew against US pilots and the nephew of the founder of the MiG Design Bureau.

This is the heart of the Z-machine ("zee machine"). Looking and sounding like something from science fiction, this is today's science fact. It's one of the research projects that might - just might, with enough funding and enough will - solve the world's energy problems. Or, alternatively, it might not. But if it doesn't there are other fusion projects waiting in the wings to secure what is probably humanity's greatest prize: freedom from our dependence on fossil fuels. From a disappointingly slow start this episode of Horizon grew into one of the most fascinating glimpses into one possible future that I've ever seen.

Documentary series that lifts the lid on some of the most incredible structures and machines in the world. This instalment looks at the Karahnjukar Hydroelectric Project in Iceland - an audacious engineering feat that includes the building of Europe's highest dam, the drilling of 30- mile-long tunnels and the construction of a gigantic underground power plant