GEOG 1112 Lecture 2: Chapter 2
Document Summary
Chapter 2: solar energy to earth and the seasons. Universe consists of at least 125 billion galaxies. Our solar system is part of the milky way galaxy. Milky way galaxy contains over 300 billion stars. Milky way galaxy: orion spur -> sagittarius arm -> milky way galaxy -> sun and solar system. Planetesimal hypothesis: gravity, the mutual attracting force of mass, caused a cloud of gas and dust to collapse into our solar system. Nebular hypothesis: the theory that the solar and stellar systems were developed from a primeval nebula. A light year is the distance that light travels in one year. The speed of light is 300,000 km/s (186,000 mi/s): 1 light-year = 9. 5 trillion kilometers (6 trillion miles) Earth"s orbit around the sun is elliptical: earth"s ellipticity changes on 100,000-year cycle. Plane of the ecliptic: plane of earth"s orbit about the sun. Average distance from earth to the sun is 150 million km.
