The plane of Earth's orbit is at an angle to a line from the Sun through S. The vertices v and v' of the elliptical projection of the path of S are projections of positions of Earth E and E ′ such that a line E-E ′ intersects the line Sun-S at a right angle; the triangle created by points E, E ′ and S is an isosceles triangle with the line Sun-S as its symmetry axis.