Unformatted text preview: 1/21/11 Quiz QuesEon #1 True or False? In science, saying that something is a theory means it is really just a guess. Astro 109 Lecture 2: Tools of the Trade Jan. 21 A. True--but a guess by a highly educated person. B. True--but it has strong support from other scienEsts. C. False--a hypothesis becomes a scienEfic theory only aIer it has been well tested. D. False--it must have detailed mathemaEcal equaEons to back it up. E. False--theories must be published, but guesses cannot. Jan. 21 Quiz QuesEon #2 What do you get when you mulEply 21022 by 41012? A. B. C. D. E. 61010 61022 61034 81010 81034 Quiz QuesEon #3 If the Moon were to move twice as far from Earth, its angular size would A. increase. B. stay the same. C. decrease. Jan. 21 Jan. 21 Key Concepts conceptual tools -- science as a way of knowing: experiments hypotheses theories Thought QuesEon The spacecraI that landed on the Moon in the 1960s and 1970s are sEll there. Can we see them from Earth? A. B. C. D. E. Yes, with the naked eye. Yes, with a telescope. No, not at all. There is no way to tell without actually looking. I don't know how to answer this quesEon. quanEtaEve tools: power-of-10 notaEon units angles Jan. 21 Jan. 21 1 1/21/11 Science as a way of knowing Science is a way of thinking much more than it is a body of knowledge. Carl Sagan Science and scienEsts ScienEsts are people, who are trying to generate knowledge. I was like a boy playing on the sea-shore, and diver9ng myself now and then finding a smoother pebble or a preIer shell than ordinary.... Isaac Newton We are driven by the usual insa9able curiosity of the scien9st, and our work is a delighKul game. Murray Gell-Mann Science: (Webster's New World Dic9onary, 2ed) "systemaEzed knowledge derived from observaEon, study, and experimentaEon carried out in order to determine the nature or principles of what is being studied" Focus on specific ideas that can be tested with reproducible experiments/observaEons. Not science: astrology invoking a supernatural event or divine interven9on Jan. 21 Science is an insEtuEon, which provides a framework for evaluaEng knowledge. There are many hypotheses in science which are wrong. That's perfectly alright; they're the aperture to finding out what's right. Science is a self- correc9ng process. To be accepted, new ideas must survive the most rigorous standards of evidence and scru9ny. Carl Sagan Jan. 21 Falsifiability No amount of experimenta9on can ever prove me right; a single experiment can prove me wrong. Albert Einstein ScienEfic Method ScienEfic theories cannot be proved only disproved can only work "to the best of our knowledge" our understanding is never complete Untenable ideas must be discarded no person is too "great" to be challenged no idea is sacrosanct if it conflicts with solid experimental evidence The "ScienEfic Method" experiments/observaEons, evidence, hypotheses, theories, laws Jan. 21 Jan. 21 PredicEon It doesn't maSer how beau9ful your theory is. It doesn't maSer how smart you are. If it doesn't agree with experiment, it's wrong. Richard Feynman Cornerstones The most incomprehensible thing about the world is that it is comprehensible. Albert Einstein A theory should explain what is already known, and predict something that is not yet known. Start with simple systems. Not everything is predictable. weather, climate, stock market, personal rela9onships, ... just too many factors Jan. 21 Causality everything that happens has a cause Universality the laws we have discovered on Earth hold everywhere and everywhen astronomy puts this to the test! Jan. 21 2 1/21/11 ScienEsts need... The most exci9ng phrase to hear in science, the one that heralds new discoveries, is not "Eureka!" but " That's funny...". Isaac Asimov Discussion QuesEon Which of the following is not a scienEfic statement? A. Pluto is more like Kuiper belt objects than like other planets. B. Planetary orbits must be circles because the circle is the perfect geometric form. C. Winter is colder than summer because the Earth is farther from the Sun. Note: this statement is scien9fic, but wrong! D. We can measure exoplanet orbits without actually seeing the planets. E. The universe is filled with an invisible substance that produces an effect similar to anE-gravity. Jan. 21 Technical skills facts, experiments, calcula9ons, ... CriEcal thinking skills judgment, logic, reading, wri9ng, ... to evaluate scien9fic evidence and arguments CreaEvity to see connec9ons (e.g., falling apple <--> planets) to develop hypotheses and explana9ons Perseverance to explore ideas, discard those proved wrong Jan. 21 Power-of-10 notaEon A convenient way to express very large and very small numbers, and to compute with them. CompuEng with powers of 10 3000000 500 = (3 106 ) (5 102 ) = (3 5) (106 102 ) = 15 106+2 = 1.5 109 = 1.5 10 108 100 101 102 103 = 1 = 10 = 100 = 1000 100 10-1 10
-2 = 1 = = = 10-3
Jan. 21 1 = 0.1 101 1 = 0.01 102 1 = 0.001 103
Jan. 21 Units SI units (metric system) length: meter or kilometer mass: kilogram Eme: second or year angle: degree, arcmin, or arcsec Example How many seconds are there in a day? 1 d 24 hr 60 min 60 sec = 86400 sec 1d 1 hr 1 min Units are as important as numbers! Always keep track of units! Convert units by mulEplying by 1. Jan. 21 Note how we can convert units. Always keep track of units! Jan. 21 3 1/21/11 Astronomers' units Length Astronomical Unit (AU) = average distance between Earth and Sun 1 AU = 1.496 108 km Astronomers' units Mass Sun M = 1.99 1030 kg MJ = 1.90 1027 kg
M = 5.97 1024 kg light-year (ly) = distance light travels in 1 year 365 d 86400 s 1 ly = 3 105 km s-1 1 yr = 9.46 1012 km 1 yr 1d
Jan. 21 Jupiter Earth Jan. 21 Angles "arcminutes" full circle = 360 "arcseconds" Jan. 21 Jan. 21 Jan. 21 Jan. 21 4 1/21/11 Angular size Angular size and distance D d D=
Jan. 21 Jan. 21 d 206265 arcsec Example The angular diameter of the Moon is about half a degree. The Moon is about 384,000 km away. What is its physical diameter? D d 206265 arcsec 60 arcmin 60 arcsec 384000 km = 0.5 deg 1 deg 1 arcmin 206265 arcsec = 3350 km = Discussion QuesEon The spacecraI that landed on the Moon in the 1960s and 1970s are sEll there. Can we see them from Earth? A. B. C. D. E. Yes, with the naked eye. Yes, with a telescope. No, not at all. There is no way to tell without actually looking. I don't know how to answer this quesEon. Jan. 21 Jan. 21 Discussion QuesEon The Moon is approximately 384,000 km away from Earth. Our telescopes can resolve objects as small as 1 arcsec in diameter. The smallest object we can resolve on the Moon is A. B. C. D. E. an astronaut's footprint an Apollo Lunar Module a crater 20 m in diameter a crater 2 km in diameter a crater 200 km in diameter D=
Jan. 21 1 arcsec 384000 km = 1.9 km 206265 arcsec 5 ...
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- b. c. d., C. D. E., A. B. C. D.