planets
The system is isolated from other masses. This allows us to neglect any small effects due to outside masses. The conditions are satisfied, to good approximation, by Earths satellites including the Moon , by objects orbiting the Sun, and by the satellites of other planets. Historically, planets were studied first, and there is a classical set of three laws, called Keplers laws of planetary motion, that describe the orbits of all bodies satisfying the two previous conditions not just planets in our solar system . These descriptive laws are named for the German astronomer Johannes Kepler 15711630 , who devised them after careful study over some 20 years of a large amount of meticulously recorded observations of planetary motion done by Tycho Brahe 15461601 . Such careful collection and detailed recording of methods and data are hallmarks of good science. Data constitute the evidence from which new interpretations and meanings can be constructed.