AST251H1 Lecture : Lecture 2, Physics and the Universe Gravity, heliocentric system, atomic spectra, composition of the universe
Document Summary
Newton: theory of gravity explains all planetary motions. Electromagnetic radiation allows us to characterize each element and molecule. Find out what the sun is made of. Speed of light c=300 000 km/s, highest possible velocity. Oort cloud, kuiper belt are found beyond the nine planets. Neptune, the last (8th) planet: 4 light hours. The oort comet cloud: extends to about a light week. The nearest star: 4 light years and 1 au as the distance from sun to earth. 1 parsec is the distance corresponding to a parallax angle of 1 arc-second. Sun is 0. 01 au in diameter; neptune"s orbit is 30 au. The nearest stars are >1 parsec or 4 ly away. Visible light images of the milky way show black blotches. 1000 ly thick by 100 000 ly diameter. Sun is in the disk, 28 000 ly out from the centre. At least 100 billion stars in this galaxy.