The Universe, Solar System, and Planets I

1. The Universe, Solar System, and Planets I

7. Origin of the Universe -Did It Begin with a Big Bang?

9. Early History of the Universe Matter as we know it did not exist at the time of the Big Bang, only pure energy. Within one second, the 4 fundamental forces were separated gravity - the attraction of one body toward another electromagnetic force - binds atoms into molecules, can be transmitted by photons strong nuclear force - binds protons and neutrons together in the nucleus weak nuclear force - breaks down an atom�s nucleus, producing radioactive decay

10. Early History of the Universe After 3 minutes, photons and neutrons began to fuse to form the nuclei of hydrogen and helium atoms About 300,000 years later, temperatures were cool enough for complete hydrogen and helium atoms to form Photons escaped from matter about the same time, and light existed for the first time

11. Changing Composition of the Universe 200 million years later, with expansion still occurring, stars and galaxies began forming from leftover matter - hydrogen and helium nuclear fusion in stars has reduced the original composition of 100% H and He to 98% when a dying star explodes, the heavier elements created by fusion are blown into space to be recycled by newly forming stars the overall composition of the galaxies is gradually changing to the heavier elements

14. General Characteristics of the Solar System Planetary orbits and rotation planet and satellite orbits are in a common plane nearly all planet and satellite orbital and spin motions are in the same direction rotation axes of nearly all planets and satellites are roughly perpendicular to the plane of the ecliptic

15. General Characteristics of the Solar System Chemical and physical properties of the planets the terrestrial planets are small, have a high density, and are composed of rock and metallic elements the Jovian planets are large, have a low density, and are composed of gases and frozen compounds

16. Meteorites - Visitors from Outer Space Stones - composed of iron and magnesium silicates, about 93% of all meteorites Irons - composed of iron and nickel alloys Stony-Irons - nearly equal amounts of iron and nickel and silicate minerals