Who invented laws of planetary motion

There are five possible Platonic solids with four, six, eight, twelve, and twenty sides. The model Kepler presented was based on a sequence of six spheres and the five Platonic solids, each located between two spheres. Thus, each sphere represented one planet. Initially, it seemed to explain the approximate ratios of the orbits of the six planets. It also gave a reason why there are only six planets—because there are only five Platonic shapes, each of which needs to fit between the orbit of two planets, only once.

Kepler published this theory in detail, in his book Mysterium Cosmographicum. Despite all the value he gave to this theory, we now know how wrong it was.

Kepler cherished the theory as his most significant work, long after he had discovered the three laws. However, the number of planets in the solar system or any other system in the universe is not predictable. Many of the numbers appearing everywhere are out of a mere accident, just like the number of planets.

Kepler thought his greatest achievement was the wrong solar system he drew, but it was the three laws that were so right to survive to date. Learn more about the cosmological constant and dark energy. At the age of 27, Kepler became the assistant of a wealthy astronomer, Tycho Brahe, who asked him to define the orbit of Mars. Brahe, who had his own Earth-centered model of the Universe, withheld the bulk of his observations from Kepler at least in part because he did not want Kepler to use them to prove Copernican theory correct.

Using these observations, Kepler found that the orbits of the planets followed three laws. Eventually, however, Kepler noticed that an imaginary line drawn from a planet to the Sun swept out an equal area of space in equal times, regardless of where the planet was in its orbit. For all these triangles to have the same area, the planet must move more quickly when it is near the Sun, but more slowly when it is farthest from the Sun. It was this law that inspired Newton, who came up with three laws of his own to explain why the planets move as they do.

By unifying all motion, Newton shifted the scientific perspective to a search for large, unifying patterns in nature. Law I. Every body perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed theron. The law is regularly summed up in one word: inertia. Law II. The alteration of motion is ever proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed.

The strength of the force F is defined by how much it changes the motion acceleration, a of an object with some mass m. Law III. You might recall from math classes that in a circle, the center is a special point.

The distance from the center to anywhere on the circle is exactly the same. In an ellipse, the sum of the distance from two special points inside the ellipse to any point on the ellipse is always the same. These two points inside the ellipse are called its foci singular: focus , a word invented for this purpose by Kepler.

This property suggests a simple way to draw an ellipse Figure 3. We wrap the ends of a loop of string around two tacks pushed through a sheet of paper into a drawing board, so that the string is slack. If we push a pencil against the string, making the string taut, and then slide the pencil against the string all around the tacks, the curve that results is an ellipse.

At any point where the pencil may be, the sum of the distances from the pencil to the two tacks is a constant length—the length of the string. The tacks are at the two foci of the ellipse. The widest diameter of the ellipse is called its major axis. Half this distance—that is, the distance from the center of the ellipse to one end—is the semimajor axis , which is usually used to specify the size of the ellipse. Figure 3: Drawing an Ellipse. Each tack represents a focus of the ellipse, with one of the tacks being the Sun.

Stretch the string tight using a pencil, and then move the pencil around the tacks. The length of the string remains the same, so that the sum of the distances from any point on the ellipse to the foci is always constant.

The distance 2a is called the major axis of the ellipse. The shape roundness of an ellipse depends on how close together the two foci are, compared with the major axis.

The ratio of the distance between the foci to the length of the major axis is called the eccentricity of the ellipse. If the foci or tacks are moved to the same location, then the distance between the foci would be zero. This means that the eccentricity is zero and the ellipse is just a circle; thus, a circle can be called an ellipse of zero eccentricity. In a circle, the semimajor axis would be the radius.

Next, we can make ellipses of various elongations or extended lengths by varying the spacing of the tacks as long as they are not farther apart than the length of the string. A planet does not move along its elliptical path at a uniform velocity; it moves more swiftly when it is closer to the Sun and more slowly when it is farther removed. Behind the nonuniform velocities, the second law finds a uniformity in the areas described in equal time intervals.

See also: Velocity. Again, Newton demonstrated the dynamic cause behind Kepler's second law. In this case, it is not restricted to forces that vary inversely as the square of the distance; rather, it is valid for all forces of attraction between the two bodies, regardless of the law the forces obey.

The second law expresses the principle of the conservation of angular momentum. If body B moves in relation to body A in a straight line with a uniform velocity, it has a constant angular momentum in relation to A and the line joining B to A sweeps out equal areas in equal increments of time.

No force of attraction or repulsion between the two bodies can alter their angular momentum about each other. The second law thus expresses a relation that holds for all pairs of bodies with radial forces between them. See also: Angular momentum. Kepler's third law states that there is a constant ratio between the square of the orbital period of a planet to the cube of the planet's semimajor axis.

The orbital period is the time required for a planet to complete one orbit, while the semimajor axis is half the length of the long axis of the ellipse, a value that is approximately equal to the mean radius, which is the average distance from the Sun during one orbit. Kepler's first two laws govern the orbits of individual planets around the Sun. His third law defines the relative scale of the system of planets. The four satellites that Galileo had discovered around Jupiter were found to obey the third law, as did the satellites later found around Saturn.

Newton demonstrated once again that the third law is valid for every system of satellites around a central body that attracts them, as the Sun attracts the planets, with a force that varies inversely as the square of the distance. Kepler's three laws of planetary motion are all premised on the phenomenon, proved by Kepler himself, that the planes of the planetary orbits all pass through the Sun some have referred to this discovery as Kepler's zeroth law.

Kepler's laws revolutionized astronomy in their recognition of the value of high-precision observation and by improving the prediction of planetary positions by a factor of With the aid of his laws, Kepler was able to predict with full confidence transits of Mercury and Venus in The Venus transit was not witnessed in Europe, even though modern calculations have shown that it should have been visible from Italy and farther eastward.