Guru, Jupiter, is the fifth graha and the great benefic of the system, also called Brihaspati after the priest-teacher of the gods, who is its presiding deity. Its gemstone is yellow sapphire, its element is ether (akasha), and its Vimshottari period is sixteen years. In jyotisha Guru signifies wisdom, dharma, teachers, children, wealth, and grace, it is the planet of expansion and blessing, and its favourable aspect is held to protect whatever it touches. Guru rules two signs, Dhanu (Sagittarius) and Meena (Pisces), and is exalted in Karka (Cancer). Because it is the natural significator of fortune and righteousness, its condition is weighed heavily for questions of guidance, prosperity, and religious life. These are the traditional significations of jyotisha; the underlying body is the largest planet, whose slow twelve-year circuit through the signs the tradition tracks.
The name graha comes from the Sanskrit root grah-, to seize or grasp, defining the class by its grip on a nativity rather than by physical status, a definition that lets Rahu and Ketu, mere calculated points, stand alongside a body as substantial as Guru within the same ninefold scheme. Jupiter's place among the classical seven reached Sanskrit astrology from Greek horoscopy through the Yavanajataka, a versification of a Greek astrological text of roughly the second to fourth centuries CE, which brought the machinery of dignity and exaltation to bodies India had already observed for millennia in its own tradition. The wisdom and grace significations attached to Guru, together with his sixteen-year Vimshottari period, belong to a later layer, codified in compilations such as the Brihat Parashara Hora Shastra, generally dated to 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