There are only a few aspects between partners that encourage potential matrimony, and even then, they can also indicate other types of commitment. In the context of this article, “marriage” refers to a mutual decision to formalize a romantic commitment in whatever spiritual or social context is meaningful. Note that all these synastry aspects can be applied to straight or same-sex couples.
Before a couple even goes near the idea of wedlock, there must be at least one Saturn connection in their synastry. Saturn interaspects can be part of any long-term relationship (co-workers, friends, parent/child), but they are absolutely essential for commitment between two people. Saturn contacts are the cement that stabilize a relationship, so marriage can be built upon it.
If your partner’s Saturn hits your relationship planets (Sun, Moon, Venus, Mars) or your angles (1st, 4th, 7th, 10th House cusps) with a hard aspect, they’ll feel a baseline responsibility to you. This sense of responsibility must be there before your partner can contemplate a long-term relationship. Trines and sextiles are weaker, but if they occur in multiples (your partner’s Saturn trines your Sun and Venus) there can still be enough glue to hold the two of you together. The feeling of commitment that Saturn creates goes both ways, but the Saturn person will feel the primary responsibility.
This “marriage asteroid” represents how someone relates to a partner in the context of a committed union. If your planet aspects your partner’s Juno, they will feel the urge to formalize the relationship. Conjunctions are strongest, although oppositions and squares can do the trick as well. Trines and sextiles are less pronounced, but can still work if they go both ways (your Juno and their Juno trines or sextiles mutual planets).
For example, your lover has Juno in Virgo. They are looking for a very specific (Virgo) type of partner: someone who will join them as they tinker with, and improve, the relationship. Your Sun conjuncts their Juno. This means that your external expression of purpose and ego perfectly matches what the Juno person is looking for in a partner. Both of you will feel that you can work (Virgo) together to create a formal union, although the Juno person will feel this most strongly.
The Sun and Moon
Your Sun conjunct your partner’s Moon (or vice versa) is the gold standard for potential marriage aspects. The Sun person’s conscious will (male energy) unites with, and is supported by, the Moon person’s emotions (female energy). There is an instinctive sense of belonging, because you and your lover complement each other at a primary level. The Sun person will usually dominate (this is true for straight and same-sex couples). For sign specific examples, check out the articles on Sun/Moon compatibility. The powerful connection created by a Sun/Moon aspect is mutual.
Sun/Moon oppositions can also create a powerful urge for marriage (you and your partner balance out each other). Squares create strong attraction, but the tension can be too jarring for settling into a long-term union. Trines and sextiles create a nice flow of energy, but aren’t strong enough (by themselves) to push the relationship forward.
The Sun/Moon Midpoint
This is the mathematical midpoint between the natal Sun and Moon. It has been referred to as the “inner marriage” between a person’s male and female energy — the union of their external purpose and internal needs. If your planet conjuncts or opposes this midpoint, you are the external manifestation of that need.
For example, your Mars conjuncts your partner’s midpoint. Through the expression of your initiative, ambition and sexuality (Mars), you are a prompt for the midpoint person. Even though your Mars energy may be aggressive, the way you express it just seems to click with your partner’s inner puzzle. When working with any midpoint contacts, only the hard aspects (squares, oppositions and conjunctions) are considered. Midpoint contacts tend to be one way, with the midpoint person feeling the effects.
The 7th House
If your planet activates your partner’s 7th House of committed relationships, they will view you as their ideal partner. If there are other aspects (in the house person’s chart) that support a desire for formal union, they may also see you as a potential spouse. A conjunction from your planet to their 7th House cusp is most powerful, but your planets anywhere in their 7th House will work. If your Jupiter falls in their 7th, your beliefs will boost their faith in committed partnerships; you’ll make the idea (of commitment to you) seem good. If your Venus activates their 7th House, the way you express love will stir your partner’s admiration, and will blend with their view of relationships. 7th House overlays are felt primarily by the house person.
Note that if only your outer planets (Jupiter, Saturn, Uranus, Neptune, Pluto) are activating your lover’s 7th House, there will need to be some other marriage aspects between the two of you. Outer planet contacts can be powerful, but they seem to stir up issues (on the house person’s side) that reach beyond the day-to-day rhythms of a romantic relationship. It’s almost too “big picture” to function on a personal level.
As always, context is everything. The above contacts increase the chances for marriage, providing both parties have the natal characteristics that indicate the desire for marriage. Although the connections described above don’t guarantee a trip to the altar (or whatever place is chosen for the ceremony), they certainly increase the odds that two people will want to take that step.