Our solar system consists of the Sun, 8 planets (the first four are rocky, the other four are gaseous), asteroids and comets.
Gravity provides the centripetal force necessary for the orbital motion of the planets, comets, moons and artificial satellites.
Two theories were proposed for the structure of the Solar System:
Acceptance or rejection of each of the two ideas depended on the social and historical context in which it was developed and proposed.
Stars – Stars are comprised mainly of hydrogen and helium, and their energy is supplied by nuclear fusion. Hydrogen atoms fuse together to form helium. Our sun has a stable size because the inward gravitational force is equal to the outward radiating pressure. This balance of gravity and pressure determines the stability of a star.
The Universe –
Structure of the Earth –
The outermost layer is called the lithosphere, and is comprised of the crust and the solid portion of the upper mantle
Earthquakes and Volcanoes – This lithosphere is cracked into tectonic plates. On plate boundaries, volcanic and seismic activity occurs. When plates slide past each other, a sudden lurch causes an earthquake. When plates slide towards each other, the less dense oceanic plates are pushed under the continental plates forming a subduction zone. The oceanic plate melts in the mantle to form lava. Pressure builds and this molten rock forces its way to the surface. A rupture in the surface occurs. This is a volcano. When plates slide away from each other, magma erupts from the gap and cools forming new rock, as is occurring on the Mid-Atlantic Ridge. Evidence for this is the symmetrical stripes of rock either side of the ridge displaying magnetic reversal.