Elliptical orbits are the paths taken by objects as they fly around a massive object, such as the sun or Earth. Such orbits are not round as is commonly supposed; instead, they orbit the massive body in the shape of an ellipse. Ellipses are like circles that have been elongated slightly, and they are also referred to as ovals.
Most astronomical objects orbit some body that it is more massive than it is. For example, the moon orbits the Earth, the Earth orbits the Sun, and the Sun orbits the galactic center. Each of these orbits take the form of an ellipse. Because these bodies do not travel in a perfect circle, they are not always the same distance from the center of their orbit or the object that they orbit. When an object is as close as it gets to the object it is orbiting, it is said to be at perihelion. By contrast, the farthest point of the ellipse from the body being orbited is called the aphelion. The orbiting object travels the fastest while it is close to the perihelion and slowest when it is at the aphelion.
Scientists classify orbits by the shape that they trace through space. Scientists use the term “eccentricity” to explain how round or oblong the orbit is. The higher the eccentricity, the more “squished” the orbit appears.