Circular orbits are rare and require perfect circumstances. Celestial bodies tend to orbit in an ellipse, with eccentricity describing the shape. Earth has the closest to a circular orbit in our solar system. The eccentricity of an orbit can have implications, such as the temperature swings between seasons.
A circular orbit is a type of orbit in which one celestial body moves in a circle around another celestial body. While drawings of orbiting objects often depict these objects in a circular orbit for the sake of simplicity, circular orbits are actually quite rare and require some sort of perfect storm of circumstances. In our solar system, the Earth comes closest to having a circular orbit, which is one reason it is habitable, and of the planets Mercury has the least circular orbit. (Now that Pluto has been downgraded, it no longer holds the title of “most eccentric orbit”.)
Celestial bodies tend to orbit in an ellipse, with the object they are orbiting around at one of the focal points of the ellipse. The ellipse can be very elongated and elongated, or closer to a circle, with the term “eccentricity” being used to describe the shape of the ellipse. An orbit with zero eccentricity is a circular orbit, while an orbit with one eccentricity would be very elongated. For reference only, the eccentricity of Earth’s orbit is 0167.
For a circular orbit to occur, the orbiting object must reach the right speed, and the interaction between the orbiting object and the object it orbits around must remain stable. This is quite rare; Earth-launched satellites, for example, usually have a more elliptical orbit because it’s difficult to drop them into a perfectly circular orbit.
A number of calculations can be used to determine the eccentricity of an orbit and to play with variables that could change the shape of the object’s orbit. These calculations can be used to analyze data about objects in other solar systems and in developing mission plans for satellites and other objects launched from Earth.
The eccentricity of an object’s orbit can have some interesting implications. For Earth, slight shifts in position relative to the Sun play a role in the seasons, but the fact that Earth’s orbit is circular in nature also prevents extremes. If the Earth had a more eccentric orbit, the temperature swings between seasons could be too great for organisms to adapt, making life on Earth impossible. The differences in orbit also explain why various celestial objects sometimes line up with each other and other times they don’t.
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