House 9 represents the broadening of one's worldview: higher education, philosophy, distant travel, beliefs, the search for meaning beyond daily life (by contrast with House 3, which covers everyday learning and short trips).
A planet in House 9 often influences your relationship to big questions, to travel, or the way you seek to give meaning to your experience.
Cadent house (with Houses 3, 6, and 12): associated in classical doctrine with adaptation and openness — House 9 comes after the angle of the Descendant (House 7) and extends the meeting with the other toward the distant, the foreign, the elsewhere.
Natural sign and ruler: Sagittarius, ruler Jupiter — consistent with the theme: Sagittarius is itself the sign of expansion and the search for meaning. See the Sagittarius entry.
Planetary joy: the Sun finds its joy in House 9 (Hellenistic doctrine) — great beliefs and the search for meaning are considered naturally favorable ground there for the solar body. See also the Sun entry, which mentions this same joy.