Space-themed music is any music, from any genre or style, with lyrics or titles relating to outer space or spaceflight. Songs or other musical forms influenced by the concept of outer space have appeared in music throughout history, both in instrumental and vocal pieces with lyrics. As early as Ancient Greece, Pythagoras believed in something called the "harmony of the spheres". He believed that since planets and the stars all moved in the universe according to mathematical equations that these mathematical equations could be translated into musical notes and thus produce a symphony. This idea was explored further throughout Western history under the theories of Musica universalis. Some more recent and widely different examples are The Planets by Gustav Holst, and the song "Space Oddity" by David Bowie. Outer space also appears as a theme in "Space Age" retro pop music, such as Stereolab's Space-Age Bachelor Pad Music. Music about outer space attracts enthusiastic listeners from all walks of life. Some have created web pages to share their interests. NASA, JPL, and the US Governmental Centennial of Flight Commission even have a webpages showcasing and discussing music about outer space. One useful example of such a web-based list is by astronomer Andrew Fraknoi; see under External Links, below, "A Catalog of Music Inspired by Serious Astronomy." Music about outer space In 1777 was the première of the opera "Il mondo della luna"("The world on the moon"), by Joseph Haydn. In 1875 was the premiere of the opera~féerie spectacle "Le voyage dans la Lune"("A trip to the moon") by Jacques Offenbach. In 1958, Karl-Birger Blomdahl composed an opera Aniara to a libretto by Erik Lindegren based on the poem Aniara by Harry Martinson, a tragedy set aboard a space ship. In 1958, Russ Garcia recorded an exotica album called Fantastica on Capitol Records that was about space travel. In 1966 Barry Gray wrote several space music pieces for the science fiction-film Thunderbirds Are Go. In 1969, The Beatles released single "Across the Universe". In 1972, Elton John released single "Rocket Man". The same year Hawkwind recorded and released the song "Space is Deep" and then performed their Space Ritual which was an opera about a crew of astronauts dreaming in hibernation. Also in 1972 Tangerine Dream released their double album Zeit, featuring space-related track titles such as Birth of Liquid Plejades and Nebulous Dawn, as well as cover art depicting a