History of Solar System formation and evolution hypotheses with Uranus having a 98° tilt. The Moon being relatively large with respect to the Earth and other moons which are in irregular orbits with respect to their planet is yet another issue. It is now believed these observations are explained by events which happened after the initial formation of the Solar System. Attempts to isolate the physical source of the Sun's energy, and thus determine when and how it might ultimately run out, began in the 19th century. At that time, the prevailing scientific view on the source of the Sun's heat was that it was generated by gravitational
Solar System model Solar System model Solar System models, especially mechanical models, called "orreries", that illustrate the relative positions and motions of the planets and moons in the Solar System have been built for centuries. While they often showed relative sizes, these models were usually not built to scale. The enormous ratio of interplanetary distances to planetary diameters makes constructing a scale model of the Solar System a challenging task. As one example of the difficulty, the distance between the Earth and the Sun is almost 12,000 times the diameter of the Earth. If the smaller planets are to be easily visible to