The Sun is considered to be strong or weak in:
LEO: (Dignity): The Sun rules fiery Leo, the sign of creative power and leadership, where its energy is believed to shine at its most radiant and steady.
Both sign and planet are associated with vitality and authority and in this respect compliment each other perfectly.
AQUARIUS:(Detriment):in Aquarius, unlike Leo, the emotions are cool and the emphasis is on raising individual consciousness in relation to the needs of society or the group as opposed to expressing individuality for its own sake.
ARIES:(Exaltation):because of its affinity with fire. The Sun is exalted in the sign of the Ram, where the need to meet life’s challanges through the assertion of will is paramount.
LIBRA: (Fall): This sign’s connection with relationship – to find oneself through others – is at odds with the solar impulse, which is to discover one’s unique potential.
Reference: The Instant Astrologer: Felix Lyle and Bryan Aspland