The Milky Way, our galaxy, is a magnificent sight in the night sky, but we know surprisingly little about it for certain. What is its shape? How many stars does it actually contain? What lies at its centre? The Gaia space telescope will answer these questions, being armed with the most advanced camera to leave our planet, and it will allow us to see our galaxy as we've never seen it before. The Sky at Night visits the factory in Chelmsford that made the astonishing sensor at the heart of the mission.

The episode begins with Tyson describing how pattern recognition manifested in early civilization as using astronomy and astrology to predict the passing of the seasons, including how the passage of a comet was often taken as an omen. Tyson continues to explain that the origin of comets only became known in the 20th century due to the work of Jan Oort and his hypothesis of the Oort cloud. Tyson then continues to relate the collaboration between Edmond Halley and Isaac Newton in the last part of the 17th century in Cambridge. The collaboration would result in the publication of Philosophiæ Naturalis Principia Mathematica, the first major work to describe the laws of physics in mathematical terms, despite objections and claims of plagiarism from Robert Hooke and financial difficulties of the Royal Society of London. Tyson explains how this work challenged the prevailing notion that God had planned out the heavens, but would end up influencing many factors of modern life, including space flight. Tyson further describes Halley's contributions including determining Earth's distance to the sun, the motion of stars and predicting the orbit of then-unnamed Halley's Comet using Newton's laws. Tyson contrasts these scientific approaches to understanding the galaxy compared to what earlier civilizations had done, and considers this advancement as mankind's first steps into exploring the universe. The episode ends with an animation of the Milky Way and Andromeda galaxies' merging based on the principles of Newton's laws.

This episode covers the nature of how life may have developed on Earth and the possibility of life on other planets. Tyson begins by explaining how the human development of writing systems enabled the transfer of information through generations, describing how Princess Enheduanna ca. 2280 BCE would be one of the first to sign her name to her works, and how Gilgamesh collected stories, including that of Utnapishtim documenting a great flood comparable to the story of Noah's Ark. Tyson explains how DNA similarly records information to propagate life, and postulates theories of how DNA originated on Earth, including evolution from a shallow tide pool, or from the ejecta of meteor collisions from other planets. In the latter case, Tyson explains how comparing the composition of the Nakhla meteorite in 1911 to results collected by the Viking program demonstrated that material from Mars could transit to Earth, and the ability of some microbes to survive the harsh conditions of space. With the motions of solar systems through the galaxy over billions of years, life could conceivably propagate from planet to planet in the same manner. Tyson then moves on to consider if life on other planets could exist. He explains how Project Diana performed in the 1960s showed that radio waves are able to travel in space, and that all of humanity's broadcast signals continue to radiate into space from our planet. Tyson notes that projects have since looked for similar signals potentially emanating from other solar systems. Tyson then explains that the development and lifespan of extraterrestrial civilizations must be considered for such detection to be realized. He notes that civilizations can be wiped out by cosmic events like supernovae, natural disasters such as the Toba disaster, or even self-destruct through war or other means, making probability estimates difficult. Tyson describes how elliptical galaxies, in which some of the oldest red dwarf stars exist, would offer the best chance of finding established civilizations. Tyson concludes that human intelligence properly applied should allow our species to avoid such disasters and enable us to migrate beyond the Earth before the Sun's eventual transformation into a red giant.

What built the Milky Way? New research might now have the answer, revealing an unlikely hero. At the heart of our galaxy sits a super massive black hole, one of the most destructive objects in the Universe. Could it be our creator?

What if we could explore the vastness of Space? Science fiction has always fed upon our need to explore – to wonder what is out there. Space journeys from Jules Verne’s earliest ideas about attempts to leave our planet, to the Star Wars far away galaxy through to Nichelle Nichols revealing how her groundbreaking role as Lt. Uhura in Star Trek led to her participation in the recruitment of NASA’s astronauts. It explores the deep sea inspiration for Avatar, finds out why Ursula K Le Guin wrote The Left Hand of Darkness and discovers how Stanley Kubrick was able to make 2001: A Space Odyssey seem so believable. In addition, the program looks at the way Dune and The Mars Trilogy embraced the challenge of world building and discusses the appeal of the beaten up ‘dirty space’ of Dark Star and Firefly. From the horrifying scenes of Alien, to the epic spectacle of Star Wars, this is a journey to the stars and the alien encounters that await us there.

An exploration of Earth's cosmic neighbourhood. Looking beyond the borders of our solar system, what's nearby in our galaxy? How do the other objects in our local area influence life on Earth? And, how did Earth's place in the galaxy make it the perfect place for the development of advanced life? Now that the Voyagers have visited the outer planets of the solar system they are heading for new adventures in places astronomers call the Oort Cloud, the heliopause, heliosheath and eventually they may encounter double stars and exoplanets, some of which may pay a visit to the solar system one day or explode showering us with radiation. If the Voyagers live so long they will experience the local fluff, local bubble and other parts of the habitable zone of the galaxy.