Geoarc

A term applied by some modern authorities to one of the house divisions of a map erected for a given moment, when there is under consideration the effect upon an individual, at a given point on the Earth's periphery, of his motion around the Earth's center - in the Earth's daily rotation. The same subdivision of the same map is called a heliarc, when there is under consideration effects based on the actual motions in orbit around the Sun, of all the planets - including the Earth. In other words, Geoarc is synonymous with House, and Heliarc with Solar House, emphasizing the character of the motion to which the subdivisions apply. A geoarc considers the Earth as a rotating body, imparting an appar- ent motion to celestial points and objects. A heliarc views the Earth as a fixed point from which one considers the effects of the actual motions of celestial objects. The heliarcs are 30° arcs measured from the Sun's position on the day for which the Figure is erected.