Neptune is the planet named after the ancient Roman god of the sea, Neptune, whose equivalent in the Greek mythology was Poseidon. Neptune was the brother of Jupiter, who presided over the realm of Heaven, and Pluto; who presided over the Underworld.
The English composer Gustav Holst wrote, between 1914 and 1916, a seven-movement orchestral suite – The Planets, Op. 32. Each movement of the suite is named after a planet of the Solar System and its corresponding astrological character.
The fifth movement of the suite has the title „Neptune, the Mystic“ and was written in 1915. Neptune was unknown in Antiquity, being discovered on 23 September 1846, by the German astronomer Johann Galle, within a degree of the position predicted by the French mathematician Urbain Le Verrier. In astrology, Neptune is associated with dreams and illusion. The planet is also associated with spirituality and religion.
Holst conceived the idea of „The Planets“ in 1913, partly as a result of his interest in astrology. The writer and journalist Clifford Bax introduced Holst to astrology, in the spring of 1913, in Majorca. Then, Holst became a devotee of the subject, studying natal charts of his friends. He also read the works of the British astrologer Alan Leo (1860-1917), author of „Practical Astrology“, „How to Judge a Nativity“, „The Key to your own Nativity“ or „What is the Horoscope and How is it Cast“.
Holst: Neptune, the Mystic