Diurnal means ‘of the quality of the day’; nocturnal means ‘of the quality of the night’. Diurnal energies relate to masculinity and the solar principle, being active, direct and expressive, whilst nocturnal energies relate to femininity and the lunar principle, being responsive, indirect, and impressive. Yin and Yang are analogous oriental terms. The characteristics of diurnal and nocturnal influences infiltrate many areas of astrological philosophy, from the alternation of the signs (usually referred to as masculine and feminine), to the assignation of planetary rulerships over the signs. Apart from the Sun and Moon each planet has two rulerships – one diurnal, one nocturnal – to recognise their expression in these altered states (for example, Mars rules Aries, its diurnal ‘house’, and Scorpio, its nocturnal ‘house’).