AST101H1 Lecture Notes - Lecture 2: International Astronomical Union, Spiral Galaxy

• School: UTSG
• Department: Astronomy & Astrophysics
• Course: AST101H1
• Professor: Bryan Gaensler

Document Summary

Solar system: sun, planets, and all of their moons, and lots of debris (comets, asteroids, dust) Universe: the totality of all space, time, energy and matter. The milky way: contains around 200 billion stars it is 1000,000 light years across, the milky way is part of the local group which has three spiral galaxies. Stars: balls of plasma which produce energy by nuclear fusion. Planets: rocky, icy, or gassy and don"t produce much energy. In 2006, the international astronomical union (iau) accepted a new definition of the term planet , adding one new criterion to the traditional definition: planets must have cleared their orbits. That is, there can"t be a lot of other stuff orbiting the parent star in orbits very similar to the planet.