Any aspect between the Sun and the Moon—the lights—is one of the most important aspects in your chart, and if it is a major aspect like the square, it is significant indeed. The square between the Sun and the Moon symbolizes a conflict between your true, inner self (the Sun), and the images and beliefs as to who you are that you've picked up and now hold to be true (the Moon). This learning may have come from your parents, others in your childhood, or through your own way of perceiving the world based on biases from past life experiences. Whatever its apparent source, the resulting tension between your will and your emotions is frustrating, and manifests as psychological problems until you resolve the underlying, subconscious conflict. Your parents (Sun is father, Moon is mother) could have separated while you were still young enough to have felt it strongly.

Childhood male/female models are usually absent, ambiguous or unacceptable, so there is often a lot of tension and/or a need to experiment in relating to the opposite sex. You may try to escape your limitations by rushing into new experiences, but lack the perseverance to carry them to a conclusion. Self-defeating habits manifesting in the Moon's house can be changed by lessons and strengths associated with the Sun's house. You may feel that everyone else around you is in the wrong (or to blame), but it is really yourself with whom you are out of touch. Until you define, focus on and persevere with your goals, until you get back in touch with your core, you will have trouble depending on yourself for long periods of time.

If your parents were emotionally or physically separated, having to split your allegiance may have become a model for you with other couples or with multiple goals, hobbies, or careers you pursue. You may find that you need to alternate your loyalties from one to the other as though your goals or friends were antagonistic to each other as were your parents to each other. If this is true for you, becoming aware that the emotional charge or orientation you place on pairs in your life, be they couples or your own pursuits, has nothing to do with them but is rather you still trying to love your parents. The awareness of this will help you to gain the emotional centeredness and perspective necessary to enjoy more than one thing or person at the same time.

It is important to consider the quadruplicity (cardinal, fixed or mutable signs) that this square is in. Mutable squares (between Gemini or Sagittarius and Virgo or Pisces) need an adjustment in thinking or attitude and are telling you that you need to change your mind about something. Cardinal squares (between Aries or Libra and Cancer or Capricorn) can be handled by appropriate action, or by changing or ceasing the way you go after or start things. Fixed squares (between Taurus or Scorpio and Leo or Aquarius) are the hardest to deal with because they symbolize your will, which is far harder to surrender or to change than thought (mutable) or action (cardinal).

My first teacher Isabel Hickey thought that squares or oppositions in mutable signs are just beginning to manifest in this lifetime and are therefore the easiest to handle. Squares or oppositions in cardinal signs, on the other hand, are carried over from our last lifetime. If handled appropriately through constructive action they won't manifest in the next life in fixed signs. And squares or oppositions in fixed signs symbolize “lessons we have failed to learn over many lifetimes, and are deeply ingrained patterns of behavior.” And because they symbolize our will and have become habituated ways of being or responding, they need a great deal of attention and self-discipline to change.

Astronomically, Sun square Moon is the "first quarter Moon" in the waxing phase when the Moon appears half full, or the "last quarter Moon" in the waning phase when the Moon also appears half full. These phases and the Sun square Moon astrological aspect occur twice every lunar month or about once every two weeks.