A105 Stars and Galaxies Essential Facts Worksheet due today First News Quiz on Sept. 5 Read units 5, 6, 10 for next week Course Organization Syllabus/OncourseOncourse Text Assigned Reading Lecture Notes Written Assignments Projects Quizzes Observing Office Hours Caty P.: Thursday, 11-noon SW 315 Tara Angle: Tues. 11-noon Weds. 2-3 PM SW 313 How will the class work? News Quiz every Tuesday best 10 of 13 Homework every Thursday best 10 of 13 Project due Nov. 30 4 observing activities (required) Exams Sept. 28 and Nov. 2 Final exam Dec. 12 First News Quiz In Class QUIZ - Sept. 5 Astronomy Magazine article on Pluto: Use the News Quiz link on Oncourse to find the article A copy of the textbook is on 2-hour reserve in the Swain West Library (2 nd floor of this bldg.) The Sun Today Solar Orbiting Heliospheric Observatory (SOHO) Orbits between the Sun and Earth, about a million miles away a constant view of the Sun Another view from Soho View of Mercury from the Solar Orbiting Heliospheric Observatory satellite Mercury Regulus Write and work with very large or small numbers without so many digits. Only one digit should be in front of the decimal. The exponent positive when the number is greater than one, negative when the number is less than one. Review Scientific Notation 43,000,000. = 4.3 x = 4.3 x Use the worksheet with the first homework for practice Powers of 10 Power of 10NotationPrefixAbbr. billion10 9 gigaG million10 6 megaM thousand10 3 kilok hundredth10 -2 centic thousandth10 -3 millim millionth10 -6 micro billionth10 -9 nanon Basic Definitions Distances Solar Radius (700,000 km) Astronomical Unit (AU) Light year Mass Earth masses Solar masses Speed Speed of light (300,000 km per second) What is an Astronomical Unit? The average distance between the Earth and Sun 150,000,000 km = 1.5 x 10 8 km 93,000,000 miles = 9.3 x 10 7 miles 8 LIGHT MINUTES Approximation Some numbers are know very accurately, but some are NOT Use an appropriate number of digits We will use approximate numbers What is a Light Year? a light year is a distance! a light year is the distance that light can travel in one year light can travel about 10 trillion km (10,000,000,000,000 km) in one year The speed of light is 300,000 km/second Basic Definitions Collections Solar system Star System Galaxy Cluster or group of galaxies Supercluster Universe Observable universe Objects Star Planet moon, satellite, asteroid, comet Nebula The star Betelgeuse is about 500 light years away from us in the constellation Orion. If this star exploded right now, how long would it be until we found out about it? a) almost immediately b) 8 minutes c) 10 years d) 500 years e) 500 light years Size and Scale know those essential facts! Beyond the Milky Way Using those essential facts! Which of the following diagrams most closely depicts the relative sizes and distance between Earth and the Moon? Modern science relies on observations and experiments! Understanding Science Purpose to understand the universe well enough to figure out the basic relationships that govern it A process for understanding and predicting will it rain tomorrow? what will be on the quiz? what will happen if? What about facts? new discoveries better data new theories facts change! The Science of Astronomy Learn what is known and what is NOT known Develop a model to explain or describe what is known Use the model to predict what is not known TEST the predictions Refine the model But science rarely proceeds in this idealized way For example: Sometimes we start by just looking then coming up with possible explanations. Sometimes we follow our intuition rather than a particular line of evidence. Testing the Predictions Experiments and Observations repeatable quantitative well defined fair Statistics evaluate the reliability of observations Examples What time is it?What time is it? Heads or tails? Laws and Theories (and models) A law is a set of hypotheses that explains WHAT is happening usually mathematical Keplers laws of planetary motion A theory is a well-developed set of hypotheses that explains why many related natural phenomena happen Einsteins Theory of General Relativity Laws and theories are both based on detailed and repeatable observations and measurements Laws and theories both yield testable predictions What is a scientific theory? The word theory has a different meaning in science than in everyday life. In science, a theory is NOT the same as a hypothesis, rather: A scientific theory must: Explain a wide variety of observations with a few simple principles, AND Must be supported by a large, compelling body of evidence. Must NOT have failed any crucial test of its validity. Is a Theory Right? Cant ever prove a theory right Does the theory make correct predictions? If it doesnt, then its wrong If its not tested or testable, its NOT a scientific theory Burden of proof is on the person making the claim Extraordinary claims require extraordinary proof (Sagan) Understanding Science Purpose to understand the universe well enough to figure out the basic relationships that govern it A process for understanding and predicting will it rain tomorrow? what will be on the quiz? what will happen if? What about facts? new discoveries better data new theories facts change! An Ongoing Process The process of science has been so successful because results are widely shared and evaluated experiments are reproduced and checked value of ideas based on observation and usefulness, not authority Criteria of Science Consistent: The results of repeated observations or experiment are more or less the same. Observable: The event under study can be observed or natural evidence must be available. Natural: A natural caused must be used to explain why or how the event happens Predictable: The natural cause can be used to make specific predictions. Testable: Predictions must be testable through observations or experiments. Tentative: Science is subject to revision and correction based on new observations Consistent Observable Natural Predictable Testable Tentative Debating Scientific Issues How do we tell who is correct? Majority vs. minority opinions Majority isnt always right Debate is a poor technique for deciding EVIDENCE and DATA How was the experiment done? Was it repeated by others Is a new theory TESTABLE? How can we distinguish science from non-science? Defining science can be surprisingly difficult Science from the Latin scientia, meaning knowledge But not all knowledge comes from science Warning Signs of Bad Science How is it announced? Is the source reliable? How good is the evidence? is it anecdotal? does it appeal to authority? does it fit what you already know? does it violate widely-accepted laws or theories? is contrary evidence ignored? What kind of reasoning is used? Can the claim be tested? The Baloney Detection Collection Phil Plait's Bad Astronomy: Home Page PLANET-DISSOLVING DUST CLOUD IS HEADED TOWARD EARTH! September 12, 2005, by Yahoo! News By MIKE FOSTER CAMBRIDGE, Mass. -- Scared-stiff astronomers have detected a mysterious mass they've dubbed a "chaos cloud" that dissolves everything in its path, including comets, asteroids, planets and entire stars -- and it's headed directly toward Earth! Discovered April 6 by NASA's Chandra X-ray Observatory, the swirling, 10 million-mile- wide cosmic dust cloud has been likened to an "acid nebula" and is hurtling toward us at close to the speed of light -- making its estimated time of arrival 9:15 a.m. EDT on June 1, The bad news is that the total annihilation of our solar system is imminent. To avoid widespread panic, NASA has declined to make the alarming discovery public. But Dr. Sherwinski's contacts at the agency's Chandra X-ray Observatory leaked to him striking images of the newly discovered chaos cloud obliterating a large asteroid. If it continues unchecked, the chaos cloud will eventually reduce our galaxy to the state of absolute chaos that existed before the birth of the universe, the astrophysicist warned. Read units 5, 6, 10 News Quiz on Tues., Sept. 5 Moon worksheet due next Thursday Assignments for next week: