Unlike Western astrology, which is Sun based, Vedic astrology is a Moon based system. The Moon or Chandra in Sanskrit, meaning illustrious, is considered supremely important because it is the indicator for the sub-conscious emotional mind. The Moon is who we think we are, but as we evolve, we come to realize that we are not our mind and we are not our emotions. The Moon is a reflection of the power of the soul or Atman, as represented by the Sun or Surya.
The Moon is what feels most like our psychology and represents our deepest feelings, creativity, imagination and moods. The Moon is the fastest moving entity in astrology and is constantly changing as it goes through its waxing and waning phases. This correlates with the fluctuations of our emotional mind which is fickle and ever changing. We can go from happy to sad instantly and angry to calm within minutes. (Of course this is where meditation and other practices can support us in stabilizing these fluctuations.)
The nature of the Moon is to connect us with the world and each other and the sign and house where the Moon is placed in the chart tells us a great deal about where we feel emotionally vulnerable, secure and connected at a heart level, as well as indicating the state of our psychology and ability to be happy. The Moon is passive, highly impressionable, and changeable and seeks emotional security and craves connection. It's energy is sattvic or peaceful, as well as tender and compassionate. The Moon is the little child inside us, or the 'you' at home, when you are alone hanging around the house, comfortable and in familiar surroundings.
Interestingly enough, although the pure Moon energy is generous, nurturing, caring and loves unconditionally, the Moon or emotional mind’s need for connection can also lead us down a path of suffering in relationships. There is a famous myth that depicts the love sick nature of Chandra (Moon) quite well, as well as showing how the emotional mind (Moon) and the intellectual mind (Mercury) although deeply connected are enemies to each other:
Brihaspati (Jupiter), the teacher of the gods, had a very beautiful wife named Tara. One day when walking, she came by Chandra’s (the Moon’s) house. When Chandra saw her, he fell in love with her immediately, and she fell in love with him. After some time passed, Brihaspati started to miss Tara and started to ask about her. When he found out that his wife was with Chandra, he sent his disciple to bring Tara back. But Tara would not come. So he sent back his disciples several times and each time they returned without Tara. After a time, Tara became pregnant by Chandra and gave birth to Budha (a.k.a. the planet Mercury, not to be confused with the other Buddha). Because of how he was conceived, Budha hated his father and as Chandra also knew that Budha is his illegitimate son, he began to hate his son, and their rivalry continues to this day. For the sin of abducting another god's consort, Brahma banished Chandra to the outer atmosphere and Tara returned to Brihaspati. Because Brihaspati or Jupiter is enemy to no one, he forgave Tara and accepted Budha or Mercury as his own. (Story courtesy of James Kelleher, “Path of Light, Volume I”)