what is the reason for the elliptical pathway of earth around sun?

Answer 1

There are 2 ways to think abut it.

One way is that the centrifugal force of the orbital motion balances the gravity of the Sun, so if the Earth is orbiting a little too slow, it falls toward the Sun. But as it falls, it speeds up which increases centrifugal force faster than the decreasing distance can increase the pull of gravity. The result is that the Earth ends up closer to the Sun but going too fast. The extra centrifugal force causes the Earth to fly away from the Sun, but as it does it slows down. And it slows faster than the rate at which gravity gets less with distance. The result is that Earth ends up farther from the Sun and going too slow, just where it started from. This repeats forever to make an elliptical orbit. The only way to get a circular orbit is for the Earth to have exactly the right speed, not even off by a millionth of a mile per hour from the right speed. That would never happen in nature, so all the orbits are more or less elliptical.

The other, more physically accurate way of looking at it is the Earth is always falling into the Sun, but the "sideways" orbital motion makes it miss the Sun to one side all the time. If it is going too slow, it doesn't quite miss the Sun enough and ends up falling a little closer. But as it falls, it speeds up. And from here on the explanation is the same as above, but it is the sideways motion allowing a continuous fall instead of a balance between gravity and centrifugal force. The reason this is more physically accurate is that centrifugal force isn't real. It is a virtual force, but that is confusing to most people not schooled in physics.

Answer 2

It's because the gravitational force of the Sun is, to a very high level of approximation, an inverse-square law. In an inverse-square law force field, the trajectories of particles (like the Earth) are always curves that are conic sections. This is a precise mathematical theorem. It must have first been proven by Newton in his Principia, although I am not sure of this. The only closed curve that is a conic section is the ellipse (a circle is an ellipse with equal axes). A parabola and a hyperbola are conic section curves that are open.

In General Relativity, the inverse-square law is shown not to be exact. Also, the inverse-square law is not precisely exact, even in Newtonian gravity, because the Sun is somewhat oblate. So the orbit of the Earth-Moon system is not precisely elliptical.

Answer 3

Newton's 1st law (Law of Inertia) - An object in motion tends to stay in motion. As the sun's gravity pulls on the earth it causes it to accelerate through space and pull it past the sun. As the Earth begins to accelerate past its orbit's closest point to the sun, the sun's gravity slows it down and pulls it back toward the sun. If gravity did not pull it back, the Earth would be flung out of the solar system in a straight line. This is because celestial objects in motion will remain in that same motion until another force (in this case gravity) act on them and alters their course. This inertial "tug-of-war" is responsible for the elliptical orbit.

Answer 4

Johannes Kepler's primary contributions to astronomy/astrophysics were his three laws of planetary motion.

Below is a link to an in depth discussion of his laws of planetary motion. When reading the info, keep in mind that a circular orbit is a special case of an elliptical orbit. When two masses in space attract each other by gravity, the likelyhood of them being in a circular orbit is very small.

Click on link below for a reference to Kepler's Laws:
http://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion

Hope this helps!

Answer 5

I guess that's because the orbital speed changes.