The Planets is an orchestral suite composed by Gustav Holst, between 1914 and 1916. It is notable for its elaborate score for large orchestra with some unusual instruments, and it represents the most-performed composition by an English composer.
The suite has seven movements, each of them named after a planet and its corresponding Roman deity (see also Planets in astrology):
The concept of the work is astrological rather than astronomical (which is why Earth is not included). The idea was suggested to Holst by Clifford Bax, who introduced him to astrology when the two were amongst a small group of English artists holidaying in Majorca in the spring of 1913; Holst became quite a devotee of the subject, and liked to cast friends' horoscopes for fun. Each movement is intended to convey ideas and emotions associated with the human psyche, not the Roman deities. Holst also used Alan Leo's book What is a Horoscope? as a springboard for his own ideas, as well as for the subtitles (i.e., "The Bringer of...") for the movements.
Pluto was discovered in 1930, four years before Holst's death, and it was hailed by astronomers as a new planet. Holst expressed no interest in writing a movement for it--as previously stated, he had become disillusioned by the popularity of the suite by that time, believing that it took too much attention away from his other works. In August 2006, the International Astronomical Union (IAU) for the first time defined the term "planet", which resulted in a change in Pluto's status, from a planet to a dwarf planet. Thus, Holst's original work is once again a complete representation of all the extra-terrestrial planets in the Solar System.