EXCENTRIC
, is applied to such figures, circles, spheres, &c, as have not the same centre; as opposed to Concentric, which have the same centre.
Excentric, or Excentric Circle, in the ancient Ptolomaic astronomy, was the very orbit of the planet itself, which it was supposed to describe about the earth, and which was conceived Excentric with it; called also the Deferent.
Instead of these Excentric Circles round the earth, the moderns make the planets describe elliptic orbits about the sun; which accounts for all the irregularities of their motions, and their various distances from the earth, &c, more justly and naturally.
Excentric, or Excentric Circle, in the New Astronomy, is the circle described from the centre of the orbit of a planet, with half the greatest axis as a radius; or it is the circle that circumscribes the elliptic orbit of the planet; as the circle AQB.
Excentric Anomaly, or A- nomaly of the Centre, is an are AQ of the Excentric circle, intercepted between the aphelion A, and the right line QH, drawn through the centre P of the planet perpendicular to the line of the apses AB.
Excentric Equation, in the Old Astronomy, is an angle made by a line drawn from the centre of the earth, with another line drawn from the centre of the Excentric, to the body or place of any planet. This is the same with the prosthapheresis; and is equal to the difference, accounted in an arch of the ecliptic, between the real and apparent place of the sun or planet. See Equation of the Centre.
Excentric Place of a planet, in its orbit, is the Heliocentric place, or that in which it appears as seen from the sun.
Excentric Place in the ecliptic, is the point of the ecliptic to which the planet is referred as viewed from the sun; and which coincides with the heliocentric longitude.
