AST101 Lecture 3 Notes

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Astronomy & Astrophysics
Dan Dolderman

Week 2 – Lecture 3 Tues. Sept. 18/12. • stars are balls of plasma which produce energy by nuclear fusion • star = producing excess energy more than they are absorbing from space (nuclear fusion), made from plasma (charged gas) • planets are rocky, icey, or grassy, and they don't produce much energy • planet – not a lot of extra energy, small spherical body, do not generate a lot of energy on their own • 3 different types of planet • saturn – gas giant planet (mostly made of liquid) • neptune – ice giant (big ball of ice in the centre) • new definition of the term “planet” ◦ planets orbit stars directly (not other planets) ◦ planets must be massive enough for their own gravity to compress them into spherical shapes ◦ 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 • the asteroid Ero can't be a planet because it's not a sphere • planets orbit stars (planets that orbit other planets are considered moons) • titan orbits saturn (same size of mercury = not planet) • pluto can't be a planet because its orbit is full of other objects (mainly comets) • pluto is a dwarf planet • pluto – orbits contains other objects (comets) and orbit isnt circular • dwarf planets: pluto, ceres (use to be considered as an asteroid), makemake, haumea, eris • moon – any large body that orbits a planet • titan, a moon of saturn • titan is bigger than mercury (titan is a moon) • nebula is a cloud of gas (bright) and dust (dark) (creates solar systems) • darkness in nebula is dust • science tests falsifiable hypotheses using the scientific method • science studies the natural world using falsifiable hypotheses using scientific method, emphasis on testing • scientific method: theory -> falsifiable hypotheses -> experiment ◦ model: astrological sun
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