The Moon is the ruling planet of Cancer. In Roman mythology the Moon is represented by Diana, the hunter goddess. The Moon is the earth's companion satellite, though some astrologers believe that it approaches being a planet in its own right. The Moon is large enough for its gravity to affect the Earth, stabilising its orbit and producing the regular ebb and flow of the tides. The Moon is familiar to us for its different phases, waxing and waning in appearance in an unchanging cycle. The Moon orbits the earth in about 28 days, spending a fleeting 2.33 days in each of the signs of the zodiac. The lunar day syncs up with its orbit around Earth in such a manner that the same side of the moon always faces the Earth and the other side, known as the "far side of the moon" faces towards space.

Astrologically the moon is associated with a person's emotional make-up, unconscious habits, rhythms, memories and moods, and their ability to react and adapt to those around them. It is also associated with the mother, maternal instincts or the urge to nurture, the home, the need for security, and the past, especially early experiences and childhood. The first-century poet Manilius, described the Moon or Luna, as melancholic. In medicine the moon is associated with the digestive system, stomach, breasts, the ovaries and menstruation (which does occur on a monthly cycle), and the pancreas. Despite Manilius' assignation, the moon is commonly associated with the phlegmatic humour; it ruled the animal spirits together with Mercury. In modern astrology, the moon is the ruler of the 4th house; traditionally, it ruled the 7th house, the house of partnership, and had 'joy' in the 3rd house of neighbours (associated with lunar themes of accommodation, change and the clan). The Moon is associated with Monday. Dante Alighieri associated Luna with the liberal art of grammar.
Full Moon

In Chinese astrology, the Moon represents Yin, the passive, receptive feminine life principle. In Indian astrology, the Moon is called Chandra or Soma and represents the mind, queenship, and mother. The north lunar node (called Rahu) and the south lunar node (called Ketu) are considered to be of particular importance, and are given an equal place alongside the seven classical planets as part of the nine navagraha. Also unique to Indian astrology is the system of 27 (or 28) lunar stations or 'mansions' called nakshatra which are believed to be of major importance in indicating the life path of the individual.