Всё, эта непроходимая дурь мне надоела. Читайте, просвещайтесь:

"If the Earth is assumed to be spherical (instead of its actual ellipsoidal shape) and if the celestial sphere is assumed to lie exactly on the planet's surface, the Ecliptic then takes the shape of a great circle that is tangent both to the Tropic of Cancer and to the Tropic of Capricorn.

Due to the Earth's movement of rotation, the Ecliptic changes place continuously, moving around the planet approximately once every day. So, if somebody wants to draw the Ecliptic on a world map he or she must choose arbitrarily the position of the points of tangency of the Ecliptic with the Tropics. By convention, mapmakers have always tended to draw the tangency points either at 0° and 180° or at 90° and 270° longitude."

(Zodiac on Earth: The Ecliptic on two sixteenth-century Ottoman World Maps)