Shukra, Venus, is the sixth graha, the second benefic of the system, named for Shukracharya, the guru of the asuras, who is its presiding deity. Its gemstone is the diamond, its element is water, and its Vimshottari period is twenty years, the longest of the nine. In jyotisha Shukra signifies love, marriage, beauty, art, pleasure, comfort, and refinement. It is classed as a benefic and is the natural significator of the spouse, particularly the wife, and of the sensual and aesthetic goods of life. Shukra rules two signs, Vrishabha (Taurus) and Tula (Libra), and is exalted in Meena (Pisces). Its condition is weighed for questions of relationship, wealth, and enjoyment. These are the interpretive conventions of jyotisha; the underlying body is the second planet, the brilliant morning and evening star long linked with beauty across many traditions.
Graha is from the Sanskrit root grah-, to seize or grasp, a name that defines the nine grahas by their hold on a nativity rather than by physical existence, broad enough to cover Rahu and Ketu, calculated points and not bodies, within the same class as Shukra, which plainly is one. Venus's inclusion among the seven classical grahas reached Sanskrit astrology from Greek horoscopy through the Yavanajataka, a Sanskrit versification of a Greek astrological text of roughly the second to fourth centuries CE, which carried the apparatus of dignity and exaltation to bodies already long known to Indian astronomy. The love, beauty and refinement readings attached to Shukra, along with the twenty-year Vimshottari period, the longest of the nine, belong to a later layer, credited to compilations such as the Brihat Parashara Hora Shastra of roughly the seventh or eighth century CE.
Sources Brihat Parashara Hora ShastraSage Parashara (attributed) with Jyotihsastra: Astral and Mathematical LiteratureDavid Pingree, The Yavanajataka of SphujidhvajaDavid Pingree