why the earth orbital motion around the sun is ellipticle?

Answer 1

As the Moon travels around the Earth, you would assume it follows a circular path. In reality, it travels in an elliptical orbit. This is true of the planets around the Sun, as well as satellites around the Earth and even electrons around an atom. The motion of objects in orbit follows the rules of the Kepler's three laws.
Ellipse
An ellipse is a geometric shape similar to an oval. It has two focus points, as seen in the picture below.
What is interesting about an ellipse is that if you made a pool table in the shape of an ellipse and hit a ball through one focus point, it would bounce off the wall and roll through the other focus point. Likewise, if the sides were reflective, light at one focus point would be reflected and focus at the other point.

A circle is a special case of an ellipse where both focus points are at the same point--the center of the circle.

Kepler's Laws
In the 16th century, Polish astronomer Nicolaus Copernicus determined that the Earth and the planets rotate around the sun. Previously, scientists thought everything rotated around the Earth. Copernicus thought the orbits were circles.

Then about 75 years later, German mathematician Johannes Kepler found that the orbits were not circles, but ellipses. He formulated laws as to how planets and other space objects travel when in an orbit. These became known as Kepler's Laws.

Kepler's first law
The first law is that the orbit of an object moving around another in space is elliptical with the stationary object located at one of the focal points of the ellipse.

In other words, the Earth travels around the Sun in an ellipse, and the Sun is at a focal point of that ellipse. The same is true for a space satellite traveling around the Earth. It is possible for a satellite to travel in a circular orbit, but that is a special case.

Kepler's second law
Kepler's second law states that the orbiting satellite will speed up when it gets closer to the object at the focus. This is caused by the increased effect of gravity on the orbiting object as it gets closer to what it is orbiting around.

The mathematical statement of the law is that the area swept by the planet or rotating object in in giving time is the same, independent of the distance to the object at the focus.



Areas swept in a given time are equal

Since the areas are equal, the arc that is further away is shorter, meaning that the speed will be slower. This is not only true for objects in space but also for electrons moving around the atom, as seen in the illustration below.



Electrons moving around an atom

You can see this effect even better in the Orbit Demonstration on the next page.

Kepler's third law
This law shows the relationship for the time required for a planet to move around the Sun and the average distance from the Sun. The relationship is that the time squared (t2) is proportional to the distance cubed (d3). Thus, if you knew the time it took to go aournd the Sun and the distance for one planet, you could find values for another.

If t = time and d = distance for one planet, and T = time and D = distance for another planet, then:

t2 / T2 = d3 / D3

Equation 1

Calculation example
Now the time (T) it takes the Earth to go around the Sun one time is about 365 days (1 year) and the distance (D) the Earth is from the Sun is about 92 million miles (1 AU or astronomical unit).

Thus T = 1 and T2 = 1. Also D = 1 and D3 = 1.

Now Jupiter's distance (d) from the Sun is about 5 times as far away or 5 AU. That means that d3 = 53 = 125. Thus the time (t) it takes Jupiter to go around the Sun can be calculated from Equation 1.

t2 / 1 = 125 / 1

Take the square root of both sides of the equation, and

t = 11.2 years

which is close to the actual length of a Jupiter year.

Applications
Kepler's Laws were used to explain the orbital motion of the planets around the Sun, as well as the various moons around the planets. You can use the laws to calculate the speed at any point, the time of rotation and distances for any objects in space. They can also be applied to the motion of electrons around the nucleus of an atom.

A good demonstration of the motion of a space satellite around the Earth according to Kepler's Laws of orbiting objects can be seen in the next page. You can adjust the shape of the orbit with a slider.

(Note that this animation will only work if your browser is Java-enabled.)

Orbit Demonstration

In conclusion
Kepler's three laws explain orbital motion. The laws are: (1) Orbits are elliptical in shape, (2) the area swept in a given time is constant for a given ellipse, and (3) the relationship for the time required for a planet to move around the Sun and the average distance from the Sun is the time squared is proportional to the distance cubed.

Answer 2

An ellipse has two focal points. You can put two nails in a board, tie a string in a circle, keep the string taut as you move the pencil to draw an ellipse.

Move the two nails closer together, and the "eccentricity" of the ellipse becomes less (approaches zero as the nails get closer and closer together).

A circle is just a perfect ellipse. Meang that the nails have gotten so close together that they're in the same place. Put the string around just one nail and put the pencil in the string. Keep the string taut, and you'll make a circle. This is just a special case ellipse with eccentricity equals zero.

Because there is nothing (that I know of) in nature that is a perfect case, the odds of a planet moving in a perfect ellipse (circle) with zero eccentricity is very slim. There is almost no chance that a planet will be found moving in a perfect circle.

Answer 3

it is only slightly elliptical, going like 1,000,000million miles. now that might sound like a **** load but its smaller than a atom to the universe.

ps. i took time to censor my word

Answer 4

All orbits are elliptical.