Why is the Earth’s Orbit Around the Sun Elliptical?

-- | December 8, 2013

Question: Why is the Earth’s revolution around the sun elliptical rather than a perfect circle? I feel like if there is the same amount of inertia and gravity acting on the Earth at all times, the revolution would end up being a circle, or at least closer to a circle than what it actually is. (Plese answer in the simplest form; I’m only in middle school) — Cheri

Answer: In fact, a circular orbit is just a special case of an elliptical orbit. Elliptical orbits are stable, possessing the same amount of total energy over the orbit as circular orbits. This is due, for example, to the fact that when the Earth is closer to the Sun in its elliptical orbit it orbits faster, while when it is further away it orbits slower, averaging to a value equivalent to that of a circular orbit. Elliptical orbits are much more general and allow for a wider range of initial conditions which existed when a planet/star system forms, thus making them a more probable solution for the properties of a planet’s orbital characteristics. If you want to see a nice historical account of how Johannes Kepler discovered the existence of elliptical orbits in the motion of the planets, see the How Stuff Works video on elliptical orbits.

Jeff Mangum

Facebook

Twitter

The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
	Founded in 1956, the NRAO provides state-of-the-art radio telescope facilities for use by the international scientific community. NRAO telescopes are open to all astronomers regardless of institutional or national affiliation. Observing time on NRAO telescopes is available on a competitive basis to qualified scientists after evaluation of research proposals on the basis of scientific merit, the capability of the instruments to do the work, and the availability of the telescope during the requested time. NRAO also provides both formal and informal programs in education and public outreach for teachers, students, the general public, and the media.
	The National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 "to promote the progress of science; to advance the national health, prosperity, and welfare; to secure the national defense..."
	AUI collaborates with the scientific community and research sponsors to plan, build, and operate cutting-edge facilities. We cultivate excellence, deliver value, enhance education, and engage the public.