Definition of Joy A term employed by some of the older authorities to indicate an affinity between certain planets and certain Signs, not necessarily of the character of Dignities. The original application of the term as anciently employed has been lost in the course of the centuries, and other meanings have been attached to the term. According to one theory a planet is in joy when, itself in debility, another planet with which it enjoys some similarity is posited in one of its Dignities. Thus Saturn was presumed to experience a sympathetic joy when Mars is in Capricorn, the Sign ruled by Saturn, and in which Mars is exalted; also that it there opposes and afflicts Cancer, ruled by the Moon. It feels a "joy" when Mercury is posited in either of its triplicities, since the Signs they rule belong to the same Triplicities: Capricorn-Virgo and Aquarius-Gemini. Also when Venus is in either of its Signs, because both trine Saturn's Signs: Taurus-Capricorn, Libra-Aquarius. A malefic experiences "joy" when another malefic afflicts either Sun, Moon, or any benefic which is in one of its Dignities. Thus Jupiter is in its joy when the Sun inhabits a Jupiter-ruled Sign - either Sagittarius or Pisces, or Cancer where Jupiter is in its Exaltation; or any Sign of its Triplicity - which includes all the Fire and Water Signs. Also when the Moon or Mars are in their respective Signs or Triplicities. Mars "joys" when the Sun is exalted; when the Moon is in her Sign, or when Saturn is in Capricorn. While not exalted in Leo, Mars was said to "joy" in the Sign, because both are of a fiery nature. The term belongs to an epoch when astrological writers were more poetic than scientific.
In short, any planet "joys" when another planet is placed in one of its Essential Dignities. Some authorities have confused this with what is termed the Thrones of the planets, viz.: the Signs they rule.
Latterly planets have been said to "joy" in certain Houses: Saturn, in the Twelfth; Jupiter, in the Eleventh; Mars, in the Sixth; Venus, in the Fifth; Mercury, in the First; the Sun, in the Tenth; the Moon, in the Third.
It is also said that the Sun and Jupiter "joy" in each other's Houses, as do Saturn and Mercury, and Venus and the Moon. All of which added together leaves the term in ill-repute, and generally in disuse among modern astrologers. The term has a certain merit and might well be restored, if confined to the congeniality of a planet in a House. In that way it can be said that Dignity and Debility result from Sign placement, and Joy from House placement.