Why planets have elliptical orbits

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Community Bot 1. James K James K Wouldn't orbits be circular if spacetime didn't bend, but gravity was instead an electromagnetically attractive force?

A marbel dropped on a rubber sheet with one through deforming it, will move circular from one perspective, but elliptically from another. Or am I wrong about this? However, in tge absence of external forces, the barycentre of the solar system moves with constant velocity, by Newton 1st law and so can be used to define an inertial frame, and it is relative to this frame that the orbits are elliptical. There are no inertial frames in which the orbits are circular.

Relativity does not change the thrust of this argument. Featured on Meta. Now live: A fully responsive profile. Version labels for answers. Linked Related 6. Why is earth closest to the sun in January?

Why is Mars closest to the Earth in August? What is accretion, and how did it form the Earth? How does accretion explain planet formation? How does accretion form planets? See all questions in The Planets. So, all ellipses have an eccentricity between 0 and 1.

Earth's orbit has an eccentricity of 0. This is why it's easy to mistake it for a perfect circle. Mercury , with an eccentricity of 0.

Kepler's Laws. Latest Gallery Images. Contact Us Privacy Policy Proud to be part of. In , Polish astronomer Nicolaus Copernicus published a mathematical treatise that promoted the idea of the Sun being the center of the solar system. But his treatment was complicated, and it was Kepler who used data to come up with the realization that the orbit of planets were ellipses.

In fact, Kepler came up with three laws. They are: 1 the orbit of a planet is an ellipse, with the Sun at one of the two foci; 2 the line connecting the planet and Sun sweeps out equal areas during equal intervals of time and; 3 the square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.

The semi-major axis is the distance from the center of the ellipse to the edge along the longest distance. In a mathematical sense, the third law is the most interesting, as it allows astronomers to relate how long it takes for a planet to go once around the Sun to its distance from the Sun. For instance, the closest the Earth gets to the Sun is 91 million miles or about million kilometers.

When the Earth is at aphelion, it is nearly 95 million miles or about million kilometers from the Sun. It also means that the foci are actually not that far apart, only about 4 million miles. To give some perspective, the radius of the Sun is about , miles and the distance between the Sun and Mercury is 29 million miles perihelion. Because the distance between the planet and Sun is smaller at perihelion than at aphelion, it must mean that the planet moves faster at perihelion. For the Earth, the difference is 30 kilometers per second at perihelion and 29 kilometers per second at aphelion, or a little over half a mile per second difference.

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