Navamsa is often regarded as spouse chart. D9 is more than simply knowing about marriage/spouse. It's the window to your soul.
D9 (navamsa) is one of the divisional charts which shows subconscious internal self or real strength of your planets, microscopic version of D1. It is the magnified essence steming out of your 9th house of dharma, higher learning and thus it's "nav" or 1/9 division (amsa) . We often check strength and position of planets in D9 along with d1(rashi chart) to arrive at the final result of a planet.
D9 is not only for spouse, marriage, children, nature and behaviour of spouse, but for life purpose, career, Luck, dharma, swot analysis, soul development,spiritual evolution, karmic debts, past life and mainly predicting life events based on vimshottari dasha. Life doesnt stop after marriage, but our life takes a different turn with new circumstances, altered behavior and challenges, why and how we see here. There are many other divisional charts that we see for different purposes which are very specific for career, kids, money and so on. But D9 has multiple uses.
1. There is much importance of D9 lagna and D9 moon as much as D1 lagna/moon to arrive at persons emotional and physical state in life.
D9 moon is the true nature of your thoughts and emotional framework.
2. D1 shows material consciousness/experiences/ inspirations and concrete reality of this lifetime while D9 shows astral consciousness/experiences/ inspirations, psycho emotional/spiritual imagery and expectations.
3. D1 shows your social material reality, what you end up doing using your skills, resources, circumstances, situations, confinements and restrictions thrown at you, D9 is the deeper truth of what you really want in this lifetime.
4. When considering effects of a planet, divisional charts are used for calculating shadbala, exaltation and debilitation. we take the houses that a planet sits in D1 as well as D9 to arrive at final mixed result.
5. When a planet is combust with Sun, its assumed very weak or almost dead but when we check D9 and if we see if Sun is atleast 2 houses away from the said planet, we consider the planet to be still alive and capable of giving some results.
6. Placement and lordship of dasha lord in D9 helps in predicting life events via vimshottari dasa system. D1, D9 and D60 charts have the highest vimsopak bal for our use (if we have accurate time).
7. Placement of D1 lagnesh, Atmakaraka, Badhakesh and trik lords in D9 tell about life purpose and challenges
8. D9 lagna, D9 lagna lord, planets in D9 lagna, placement of Saturn, Rahu, Ketu will tell about significant lessons to be learnt in this lifetime.
9. Past bad karmas in relationships and its effect on present relationships can be seen by the placement of mars, venus and Jupiter in D9 in comparison to D1.
10.D9 lagna and its lord shows your core attitude, behaviour, hidden assumptions and psychic expectations towards marriage and the challenges and the changes you face being married.
11.10th lord of D9 and planets placed in it shows your career path, checking the 10th lord of D1 in D9 can give clues regarding type of career, challenges, development issues in this regard.
12. Though some astrologers do not work as psychologers and focus only on telling external problems based on D1, the solution of your problems in usually found in D9 (the internal hurdles). Thus its best to read D1 along with D9 for effective remedies.