Using exact observation Brahe discovered the orbit of Mars. His hypothesis is: first is the circular orbit. After four years of research and testing 70 different combinations, circle and epicycles, he invented a kind of shape, Mars orbit. However, this model is suitable for the accurate, only as a degree. (44) Kepler know Brahe observation can be used to develop .
More accurate than the orbit of shape. Kepler finally decided to try all kinds of circular orbit. This implies that the speed change its planets around oval. Nine years later, he found the path observed elliptical orbit is good to Mars. He found the shape, not only to Mars, and every work already observed Brahe planets.Observational studies not doing the .
Experiment. According to the definition, observational study of operation experiment. Bacon in addition, observational study often involved in biological systems quantitative variable challenge. However, observational study used because it is sometimes difficult (too expensive, or too much time) or unethical longitudinal experiment and human or animal subjects. In this case, the value of observational studies, because they often suggest hypothesis .