AST 251H1 Midterms notes.docx

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Astronomy & Astrophysics
Course Code
Paola Rodriguezhidalgo

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AST 251H1 Life on Other Worlds Week 1: What is science? Scientific Method: 1. Make observations (Look) 2. Ask a question 3. Suggest a hypothesis (Come up with rules) 4. Make a prediction (Look more carefully/differently/elsewhere to test rules) 5. Perform a test: experiment or additional observation • If rules work, repeat step 3 If rules fail, go back to step 2 • Hypothesis: tested observationally/ experimentally • Model: system of hypotheses and produces specific, testable predictions • Theory: A system of models which are known to work • Law: a theory which explains many experiments Science: • Seeks explanations for observed phenomena that reply solely on natural causes • Progresses through creation & testing of models of nature that explain the observations simply • Makes testable predictions about natural phenomena. Model must be revised or abandoned if predictions do not agree with observations. Occam’s Razor: “The simpler of two models or hypothesis is the ‘better’ one” Week 2: Full cosmic address & the Universe. • Toronto, Canada, North America, Earth, Solar System, Milky Way, Local Group, Universe • Universe: the totality of all space, time, energy, & matter; ~13.8 billion years old • AU: ~1.5 * 10 km • Light year: distance light travels in 1 year; 9.46*10 km Universe Calendar: (37.8 million years/day; 1.58 million years/hour; 438 years/second) • Jan 1 : Big Bang st • May 1 : Milk Way formed • Sept 14 : Earth formed • Sept 25 : Early life on Earth nd • Oct 2 : Oldest rocks known on Earth • Dec 17 : Cambrian explosion th • Dec 26 : Rise of dinosaurs • Dec 30 : Extinction of dinosaurs • Dec 31 :t o 9:00PM: Early hominids evolve o 11:58PM: Modern humans evolve o 25 seconds ago: agriculture arises o 11 seconds ago: Pyramids built o 1 second ago: Kepler and Galileo show Earth orbits Sun • Stars: self-luminous celestial body of plasma held together by its own gravity; energy generated by nuclear reactions in interior is balanced by outflow of energy to the surface; inward directed gravitational forces are balanced by outward directed gas and radiation pressures o High temp & high density causes plasma particles “fuse” together in nuclear reactions o Generate energy by fusing hydrogen into helium and then to carbon • Nebula: cloud of gas (bright) and dust (dark) • Planets: rocky, ice, or grassy & do not produce much energy; spherical object which cleared their orbit (cannot orbit another planet/other than Sun) • Inner solar system (terrestrial): Mercury (0.4 AU), Venus (0.7 AU), Earth & Mars(1.5 AU) (small, rocky, thin atmosphere) • Outer solar system (Jovian): Jupiter (5.2 AU), Saturn (9 AU), Uranus (20 AU), Neptune (30.1 AU), other dwarf planets & comets (large, liquid + gas, small rocky core, many moons) Week 3: Habitability: basic characteristics needed & what determines life. • Conditions for habitability on Earth o Right temperature (distance from Sun & planet’s size) o Abundant water o Atmosphere o Stable environment • Volcanism: outgassing: source of atmosphere & oceans, heat & environment for primordial life • Plate tectonics: long-term climate stability by recycling rock between surface and interior • Magnetic field: protects atmosphere from solar winds • Solar system: formed 5 billion years ago • Prograde motion: Mercury, Earth, Mars, Jupiter, Saturn, Neptune • Interstell
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