Gensahar (jawzahar)
Definition
Gensahar (Arabic jawzahar, جوزهر) is the medieval term for the point where a planet's orbit crosses the path of the Sun — the ecliptic — so that the planet passes from the south side of that path to the north, or back again. It is the planet's ascending or descending node. In Arabic-Persian tradition the word most often names the Moon's two nodes, the Head and Tail of the Dragon, but Bonatti applies the same term and geometry to every planet, using a planet's gensahar to fix when it stands north or south of the Sun's path.
In Tradition
The Arabic-mediated Latin tradition treats the gensahar as the reference point for a planet's latitude — its distance north or south of the ecliptic. A planet is reckoned northern once it crosses beyond its gensahar toward the north, and southern once it crosses the opposite point of contact. Bonatti subdivides this into four positions measured in signs from the node, since whether a planet rises or falls in latitude was held to bear on its condition.
In Practice
To place a planet by its gensahar, find where its orbit cuts the Sun's path and on which side it currently lies. From the ascending crossing-point, the first three signs of travel make the planet northern-ascending and the next three northern-descending; from the descending crossing-point, the first three signs make it southern-descending and the next three southern-ascending, returning it to the gensahar where it began. Read a planet on the northern, ascending side of its path as climbing in latitude and a southern, descending one as falling. Apply the same scheme to the Moon's own gensahar, where the ascending node is the Head of the Dragon and the descending node the Tail. Use the position as one accidental consideration of a planet's condition, weighed together with its dignity, its house, and its relation to the Sun's beams, rather than as a judgment on its own.
Historical Origin
The doctrine is set out in Guido Bonatti's Liber Astronomiae (c. 1277, Vol XI Part III Second Part, the chapter "Concerning When Planets are Northern and When Southern"), preserved in Robert Hand's Project Hindsight translation, whose note identifies the gensahar as a geocentric description of the planet's ascending node. The Arabic term jawzahar underlies it and runs through the wider Arabic-Persian astronomical tradition, including Abu Ma'shar and al-Biruni, where it most often names the lunar nodes.