Marriage is a Libra/7th house affair. Most people who get married have their Sun opposite their partner's Ascendant or Rising Sign. Sun conjunct the Moon is also important. Usually it's the woman's Ascendant opposite the man's Sun and the man's Moon conjunct the woman's Sun, but it can work the other way around as well.

Then there is Moon/Moon for emotional compatibility, Mercury/Mercury for mental compatibility, and Venus/Mars for sexual compatibility. I have written about this extensively in my other synastry articles.

In the end, however, true and enduring compatability lies with the Sun signs. The other comparisons support or detract from this.

One would think the opposition and trine between Suns are the strongest marriage links. and this does often happen, but I have found that the sextile is often the best. Signs in sextile (two signs apart) are both harmonious and different at the same time. It's a lesser version of the opposition. Examples: Aries and Gemini or Taurus and Cancer. They balance or complement one another in a nice way without over-intruding and are excellent links in either marriage or friendship.

Some sextile relationships keep popping up more frequently than others like Gemini and Leo or Cancer and Virgo. I personally know of three Cancer/Virgo marriages, and in all three it's the Virgo male and the Cancer female. What is it about these two Sun signs that brings them together so often? The Virgo male is hardworking and practical providing the stability and security that the Cancer female seeks and the Cancer female is sensitive and caring providing the understanding, femininity, and domesticity the Virgo male appreciates.

While Sun sextile Sun is a wonderful indicator of marriage or partnership it is not without its problems. Both elements are very different and need some effort or work to succeed. There is much freedom and communication (Aquarius and Gemini are the natural sextile signs) with this aspect and it needs to be exercised and respected. There is much agreement and problems can easily be worked out, so long as they are open and honest with each other.

While the other Sun to Sun aspects can succeed in a marriage it is usually because the other basic supponting factors (Sun/Ascendant, Moon/Moon, Mercury/Mercury, Venus/Mars) are very strong. If the Suns are incompatible, however, the relationship will, with time, be less than satisfying and unlikely to last. This is because the Sun is your deepest self or yearning. It is your spiritual or root core. You don't want to be heading in different or conflicting directions.

Sun sextle Sun provides a solid and serious base for a fruitful and long lasting relationship. The trine is also good, especially for love and romance, but there may be too many similarities. The opposition can be very good or very bad depending on the rest of the chart. The square is usually difficult but can be important as in parent or boss, and the quincunx and semi-sextile are usually negative or irritating. With the sextile there are enough similarities but also enough differences to make the relationship different, special, and interesting.