Why do planets have elliptical orbits?
In: Physics
Gravity follows an inverse-square law, so the strength of gravity is inversely proportional to the square of the distance between the two masses. When you crunch the numbers on this, all possible orbital paths turn out to be conic sections.
A conic sections is just the surface you get if you chop through a(n infinite) cone with a plane. There are four of these. Cut horizontally and your get a circle. Cut at a slight angle and you get an ellipse. (A circle is really just a special ellipse.) Cut at an angle parallel to the slope of the cone and you get a parabola. Cut steeper, and you get a hyperbola.
The first two of these are closed curves, i.e. they are loops. These are the orbits that planets have. The other two are open curves (i.e. they go off to infinity). These are the orbits that some comets have if they pass the sun once and never return.
Latest Answers