AST101H1 Lecture Notes - Lecture 3: International Astronomical Union

• School: UTSG
• Department: Astronomy & Astrophysics
• Course: AST101H1
• Professor: Eryan Apsnler, Michael Reid

Document Summary

A light year" (ly) is a measure of distance, not time; it concerns the distance light travels in a year. 1 ly = ~63k au; 1 au = ~8 light minutes. Light is the fastest thing in the universe. Stars are balls of plasma (very hot gas) which produce energy by nuclear fusion. Planets are bodies that can be composed of many kinds of matter (rock, ice, gas, liquid), but do not produce much energy compared to stars. 2006: international astronomical union (iau) accepted a new definition for the term planet", which added another criterion to the traditional definition. Planets must be massive enough for their own gravity to compress them into spherical shapes. Planets must have clear orbits; if not, a planet must be the most dominant object in its orbit. Planets that meet the first 2 criterion but fail to meet the third criterion are called dwarf planets". Moons are any large bodies that orbit planets.