AST201H1 Lecture Notes - Lecture 18: Orbital Speed, Orbital Period, Semi-Major And Semi-Minor Axes

• School: UTSG
• Department: Astronomy & Astrophysics
• Course: AST201H1
• Professor: Macdonald

Document Summary

What are galaxies made of? stars - visible and near ir light gas - emission lines dust - far ir light. Orbital period time it takes to complete one orbit. Sun"s orbital period is 230,000,000 years came up with an accurate description of the motion of the planets. Johannes kepler: worked from tycho brahe"s data. Kepler"s 1st law: planets orbit the sun in an elliptical pattern, with the sun at one focus. Kepler"s 3rd law: more distant planets orbit slower. Planet"s orbital period depends on its distance from the sun as p2=a3. Isaac newton: revolutionized math and science, co-invented calculus. P: how long the orbit takes ( period : a: the sami-major acid, m: mass, wide orbits: slower, more mass: faster. If we know the earth"s orbital period and its orbital semi-major axis, we can calculate: the mass of the earth+sun.