In modern Western astrology, the Sun is commonly used as a symbol of identity and the Moon as a symbol of needs and habits. Sun–Moon synastry compares those positions across two charts. It offers a vocabulary for reflection, not a validated test of emotional compatibility.
There are two separate comparisons
Person A's Sun with person B's Moon is different from person B's Sun with person A's Moon. A conjunction in one direction does not imply a conjunction in the other. Record both before interpreting either.
Use the same zodiac convention for both charts and retain the degrees. A shared sign alone does not tell you the orb. For the calculation method, see Synastry Aspects.
Worked example
Suppose the recorded positions are:
- A's Sun: 10° Aries, or 10° longitude.
- A's Moon: 20° Virgo, or 170° longitude.
- B's Sun: 20° Cancer, or 110° longitude.
- B's Moon: 12° Aries, or 12° longitude.
A's Sun and B's Moon are 2° apart: a conjunction with a 2° orb. B's Sun and A's Moon are 60° apart: an exact sextile. Under an illustrative 3° allowance both count, but they are different aspects with the symbolic roles reversed. These invented positions illustrate arithmetic, not an observed relationship.
What the main aspects are used to discuss
- Conjunction, 0°: readers may explore overlap between one person's self-expression and the other's needs. It does not prove instant recognition or a past-life bond.
- Sextile, 60°: a prompt to discuss opportunities for cooperation. Cooperation still requires participation.
- Square, 90°: a prompt to ask where goals and needs differ. The chart cannot determine whether actual conflict exists.
- Trine, 120°: traditionally associated with ease. It does not mean emotional communication takes care of itself.
- Opposition, 180°: a prompt to discuss contrasting approaches without assuming that opposites attract.
Use degrees rather than assigning an aspect from elements alone. Two positions can occupy signs of the same element while falling outside the selected trine orb. Conversely, a near-boundary aspect may connect signs that a simple sign-pair rule would miss.
Turn the example into a conversation
For A's Sun conjunct B's Moon, ask each person how they prefer to give and receive support. A might enjoy public encouragement while B prefers a private conversation. Their answers can differ even when the aspect is close. That is a useful observation, not a failure by either person to live out the chart.
For the reverse sextile, ask whether they can make room for each other's routines. Do not assume the two aspects combine into a numerical compatibility score.
Moon–Moon and missing aspects
A Moon–Moon comparison uses the same geometry with both Moon positions. Readers often use it to discuss habits or comfort. No Moon–Moon aspect, or no Sun–Moon aspect, does not indicate a missing emotional bond. Changing the permitted orb can also change whether an aspect is listed.
If a birth time is uncertain, the Moon's degree may be uncertain enough to alter a close-orb result. State the uncertainty; do not present a guessed time as an exact chart. Rising-sign comparisons are especially sensitive to birth time.
Reference and limits
Astrodienst's aspect reference supplies the terminology for the angular relationships. The interpretation prompts here are editorial examples, not evidence that those angles cause feelings. Mutual consent, respectful behaviour, and the people's own accounts are more informative about their relationship than any single aspect.