Unfortunately, we do not have time in this course to explore in detail the myriad of discoveries leading to our current understanding of the universe size and age. But I do encourage you to take an astronomy class or explore some of the additional resources listed at the end of this unit.

We are now going to focus on Earth’s neighborhood, the solar system. The model we use to explain the formation of the solar system (and, in fact, the formation of any star system) is the Nebular Theory. According to this theory, the sun, the planets, and all the celestial objects in the solar system evolved from a cloud of dust and gas called a nebula.

The nebula most often results from the explosion of an aging star that turns into a supernova. Over time, the dust and gas particles in the nebula become gravitationally unstable and collapse into a rotating disk. Because the “dust” particles are more dense, their gravitational attraction is more intense and they concentrate in the inner sections of the disk. “Gas” particles (volatile material), on the other hand, are less dense and concentrate in the outer sections of the disk. Dust particles will eventually coalesce to form the rocky inner planets (also called terrestrial planets) while the gas particles coalesce to form the gas giants (also called Jovian planets).

The short videos below will demonstrate the formation of the solar system according to the Nebular theory.

Video: "The Nebular Theory" (3:05)

Video: "Formation of the Solar System" (4:27)

Video: "Introduction to the Solar System" (10:16)