Johannes Kepler published 2 laws in Astronomia nova seu Physica coelestis (1609) and a third law 10 years later in Wereldharmonie. These laws are very interesting, but I actually wonder how Kepler arrived at these laws. In other words, I consider the evidence of the laws to be at least as important as the laws themselves.
First law being :
Kepler’s first law states that all planets move around the sun in elliptical orbits, with the sun at one of the focal points of the ellipse.
Second law being:
The speed of a planet in its orbit changes in such a way that in equal time intervals the area covered by the straight line (vehicle radius) between the sun and the planet is equal. The feed ray therefore describes equal areas in equal time intervals, also called beds, hence the name of the bed law. In the example shown, the average speed of the planet in the interval AB is therefore smaller than in the interval CD. This also shows that the magnitude of a planet’s orbital velocity is not constant.
Third law being:
The square of a planet’s orbital period
Answer
Dear Lars,
Kepler has not come through proofs to his three laws. In fact, based on the observations of the planets by the Danish astronomer Tycho Brahe, he came to the conclusion that there was a system in the way in which the planets move: the movement always complied with the laws he subsequently published.
The proof of these laws was only given about a century later, and that was by a certain Isaac Newton: two bodies attract each other with a force proportional to the product of their masses and inversely proportional to the square of the distance between them (Newton’s universal law of gravity). Combining this law mathematically with his second law (force is mass times acceleration), Kepler’s laws can be proved.
Kind regards,
Answered by
Laurent Vanbeylen
Pleinlaan 2 1050 Ixelles
http://www.vub.ac.be/
.