An ellipse is a curved shape formed by all points where the sum of distances to two fixed points (foci) is constant.
An ellipse resembles an elongated circle. It has two axes: the major axis (longer) and minor axis (shorter). The eccentricity e (0 ≤ e < 1) measures how elongated the ellipse is, with e = 0 being a perfect circle. Ellipses are the shapes of planetary orbits (Kepler's First Law) and are used in optics (reflective property), satellite dishes, and whispering galleries.
Ellipses were studied by Greek mathematician Menaechmus (350 BCE) and later by Apollonius of Perga in his work on conic sections (200 BCE). Johannes Kepler discovered that planetary orbits are ellipses in 1609, revolutionizing astronomy. The reflective property of ellipses was used in the design of whispering galleries like St. Paul's Cathedral in London.