Free Sun/Moon Midpoint Calculator

A Sun/Moon midpoint calculator finds the exact halfway degree between your natal Sun and Moon. Astrologers call it the lunation point or the inner marriage because it is the degree where conscious will and emotional core fuse, making it one of the most sensitive points in your chart for relationships and identity. In synastry, another person's planets in tight aspect to this degree mark the bonds that register as fated rather than incidental.

That is the short version. The longer version is more interesting. The Sun is the part of you that wants to be visible. The Moon is the part that wants to be safe. Most of the time, those two impulses pull in different directions, which is why you can simultaneously want to give a keynote and never leave your apartment. The midpoint between them is the degree where the two finally agree.

Reinhold Ebertin, the German astrologer who built modern midpoint practice in the 1940s, called this the lunation point. Practitioners since then have called it the marriage midpoint, the inner marriage, or, when they are being florid, the axis of personal destiny. Whatever you call it, anything that touches it (a transit, a progression, a partner's Venus) tends to register as personally consequential.

There are two midpoints between any two planets, an immediate one and an opposite one across the chart. Cosmobiologists treat them as functionally equivalent for hard aspects, so you only need the shorter arc.

1. Convert each planet's position to absolute zodiac degrees, where Aries 0° = 0 and Pisces 29° = 359°
2. Add the two values
3. Divide by two (use the shorter arc when the difference exceeds 180°)
4. Convert back to sign and degree

Worked example. Sun at 16° Leo (4 × 30 + 16 = 136°). Moon at 8° Cancer (3 × 30 + 8 = 98°). Sum 234°, halved to 117°, which is 27° Cancer. The opposition is 27° Capricorn; either point reads.

Use the synastry panel above to enter two charts. The tool calculates each midpoint and scans the partner's Sun, Moon, Venus, Mars, Saturn, Ascendant, and Midheaven for hard aspects within cosmobiology orbs. What you are looking for, in roughly this order:

1. Their Sun on your Sun/Moon midpoint, or yours on theirs. The classic. The owner of the activated midpoint is typically the more attached partner.
2. Their Moon on your Sun/Moon midpoint. Domestic and emotional. Less spectacular than the Sun contact, more durable.
3. Venus, Mars, or Saturn from one chart on the midpoint of the other. Rose Murray catalogs these in When Planets Promise Love as the planetary set most likely to mark commitment relationships. Saturn especially: Saturn on your inner marriage point binds the partner to a structural promise, for better and for worse.
4. Their Ascendant or Midheaven on your Sun/Moon midpoint. Angle contacts reshape how you show up in the world together.
5. Mutual activation. When both midpoints are activated, the bond is symmetrical. Asymmetric activation is more common and not a problem; it just means one of you is the gravitational center.

We use conservative midpoint orbs inspired by cosmobiology practice rather than the wide orbs typical of natal aspect tables. Wider orbs flood the result with noise; tighter orbs surface the contacts that actually carry weight in lived relationships.

• Conjunction or opposition with Sun, Moon, or angle: 1°30'
• Conjunction or opposition with Mercury through Pluto: 1°00'
• Square: 1°00'
• Eighth-harmonic aspects (semi-square 45°, sesquiquadrate 135°): 30'

A natal degree is a fact. A transit is the weather hitting that fact. The slower the transiting planet, the longer the activation, and the more permanent the consequences.

• Saturn by hard aspect marks commitment, formal partnership, or the moment a relationship reveals what it actually is. Roughly 18 to 24 months from first hit to last.
• Uranus produces the disruption story: meeting someone unexpectedly, breaking off something stable, sudden marriage, sudden divorce. About a year of activation.
• Neptune dissolves and idealizes. Spiritual partnership, infatuation, deception, or the quiet sense that the relationship has changed shape without anyone naming it. Two to three years of contact.
• Pluto rewrites you through the relationship. The slowest and most thorough of the four. Multi-year.
• Progressed Moon crossing the midpoint marks emotional readiness windows roughly every 27 years.

Foundational references: Reinhold Ebertin The Combination of Stellar Influences, Rose Murray When Planets Promise Love, Noel Tyl Synthesis & Counseling in Astrology.

Computational defaults: ephemeris from NASA's ANISE toolkit with JPL DE-440 kernels. House placement uses Whole Sign by default, calculated from your Ascendant. The midpoint and its 180° opposite are treated as functionally equivalent for hard-aspect reading, following cosmobiology convention. For the full midpoint tree across all planet pairs, see the all astrology midpoints calculator.