Why, when the planet is accelerated during the ‘close phase’ of its orbit, isn’t it then flung away? I get that gravity pulls/holds it in orbit but why hasn’t it flattened out into a spherical orbit?
In: 5
>Why are planets orbits elliptical and not circular?
Planetary orbits are elliptical because of the nature of gravity. Sir Isaac Newton discovered that the force of gravity between two objects depends on the *square* of the distance separating them.
What does that mean? To put it simply, let’s say that a planet and its sun are at a certain distance X from each other, and the force of gravity has been calculated to be Y. The precise numbers don’t matter, only the relationship between them.
If the planet is suddenly moved to be twice as far (the distance is now 2X), then we will find that the force of gravity drops to one-quarter (the force is now Y/4). We increased the distance by a factor of two, and so the force falls by a factor of 4, because 2^2 = 4.
Because of this changing force of gravity, you can use a branch of mathematics called *calculus* (something else Newton developed) to chart out the orbital path of anything you like, and you’ll find that most orbits are indeed elliptical.
Obligatory pedantry note: Circles are ellipses, too, just with an eccentricity of 0.
Latest Answers