. . Ellipse According to Johannes Kepler, all planets in the solar system revolve around Sun in elliptic orbits with Sun at one of the foci. Some comets have elliptic orbits with Sun at one of the foci as well.
E.g. Halley’s Comet that is visible once every years with e » in elliptic orbit (Fig. . ).
Our satellite moon travels around the Earth in an elliptical orbit with earth at one of its foci. Satellites of other planets also revolve around their planets in elliptical orbits as well. Elliptic arches are often built for its beauty and stability. Steam boilers are believed to have greatest strength when heads are made elliptical with major and minor axes in the ratio : .
Fig. . The elliptical orbit of Halley’s Comet Neptune years Earth Sun Jupiter Uranus - - In Bohr-Sommerfeld theory of the atom electron orbit can be circular or elliptical. Gears are sometimes (for particular need) made elliptical in shape.
(Fig. . ) The shape of our mother Earth is an oblate spheroid i.e., the solid of revolution of an ellipse about its minor axis, bulged along equatorial region and flat along the polar region. The property of ellipse, any ray of light or sound released from a focus of the ellipse on touching the ellipse gets reflected to reach the other focus (Fig.
. ), which could be proved using concepts of incident rays and reflected rays in Physics. An exciting medical application of an ellipsoidal reflectors is a device called a Lithotripter (Fig. .
and . ) that uses electromagnetic technology or ultrasound to generate a shock wave to pulverize kidney stones. The wave originates at one focus of the cross-sectional ellipse and is reflected to the kidney stone, which is positioned at the other focus. Recovery time following the use of this technique is much shorter than the conventional surgery, non-invasive and the mortality rate is lower.