The actor shares his passion for the Cassini mission which studied Saturn and its moons.
The actor recalls reciting Lollingdon Downs for Patrick Moore shortly before his death.
Melvyn Bragg examines the Prussian naturalist and explorer, Alexander Von Humboldt.
Jerry Brotton looks at Sir Walter Raleigh's quest for gold
Raleigh tries to persuade Elizabeth I that the North American settlements were a success.
The man who predicted deforestation and harmful human-induced climate change 200 years ago