Cassini oval

The points whose distances to two fixed points, the foci, multiply to the same number b². With e = b/a below 1 it is two loops, one around each focus; at e = 1 it is the lemniscate of Bernoulli, and above 1 a single loop, pinched at the waist until e reaches √2. Cassini proposed it in place of Kepler’s ellipse for the Sun’s motion as seen from the Earth.

((x - a)² + y²)((x + a)² + y²) = b⁴

On mathcurve.com as Ovale de Cassini