The Universe is a vast endless space which includes galaxies, stars, planets and other forms of matter and energy. This chapter covers the theories of the origin of the Earth and the Universe, stars and constellations, the Solar system (Sun, planets, dwarf planets, satellites, asteroids, comets and meteors), the shape and motions of the Earth, seasons, eclipses and time zones.
1. Theories of the Earth's Origin
- Nebular Hypothesis: an early, popular argument by the German professor Immanuel Kant; revised by the mathematician Laplace in 1796. Planets were formed out of a cloud of material associated with a youthful, slowly rotating sun.
- Accretion theory: propounded by Lyttleton. About 4.6 billion years ago the solar system was a cloud of dust and gas called a solar nebula. As it spun, gravity collapsed the materials and formed the sun in the centre; the remaining materials clumped into larger particles.
- The solar wind swept lighter elements (hydrogen, helium) away from the closer regions, leaving heavy rocky materials to form planets like the Earth; farther away, lighter elements coalesced into gas giants.