Imagining an elongated right triangle in space, where the shorter leg measures one au (astronomical unit, the average Earth – Sun distance) and the subtended angle of the vertex opposite that leg measures one arcsecond (1 ⁄ 3600 of a degree), the parsec is defined as the length of the adjacent leg. The value of a parsec can be derived through the rules of trigonometry. The distance from Earth whereupon the radius of its solar orbit subtends one arcsecond.