The Regiomontanus house system divides the equator into 12 equal parts, starting from the ascending degree. Then a line is drawn through each point connecting North and South.

Such a dividing line is called a *house arc*. Its intersection with the plane of the ecliptic measures the cusp of the corresponding house.

If we take a planet and draw a line through it according to the same logic above, then such a line will be called a *circle of position*.

The intersection of the circle of position with the equator is called the *mundane position of the planet*. The mundane position's right ascension is called *oblique ascension on its horizon*. The horizon is the circle of position.