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Published on November 13, 2007

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ASTRO 101:  ASTRO 101 Principles of Astronomy Instructor: Jerome A. Orosz (rhymes with “boris”) Contact::  Instructor: Jerome A. Orosz (rhymes with “boris”) Contact: Telephone: 594-7118 E-mail: orosz@sciences.sdsu.edu WWW: http://mintaka.sdsu.edu/faculty/orosz/web/ Office: Physics 241, hours W TH 3:30-5:00 Text: “Perspectives on Astronomy” First Edition by Michael A. Seeds & Dana Milbank. :  Text: “Perspectives on Astronomy” First Edition by Michael A. Seeds & Dana Milbank. Course WWW Page:  Course WWW Page http://mintaka.sdsu.edu/faculty/orosz/web/ast101_fall2007a.html Note the underline: … ast101_fall2007a.html … Also check out Nick Strobel’s Astronomy Notes: http://www.astronomynotes.com/ Homework:  Homework Assigned question due September 6: Question 13, Chapter 2 (Why are the seasons reversed in the southern hemisphere relative to the northern hemisphere?) Coming Up::  Coming Up: Outline of Scientific Method Introduction to the Sky Constellations Stellar Brightness The “clockwork” of the sky Day/night Phases of the moon The seasons Solar and Lunar Eclipses Questions for the Day:  Questions for the Day What is the shape of the Earth, and is it stationary? http://www.alaska.net/~clund/e_djublonskopf/Flatearthsociety.htm http://fixedearth.com Questions for the Day:  Questions for the Day What is the shape of the Earth, and is it stationary? We all know the answers to the above, but can you give evidence for the correct conclusion without using modern technology? Next::  Next: The Scientific Method Outline of the Scientific Method:  Outline of the Scientific Method Outline of the Scientific Method:  Outline of the Scientific Method Gather data, make observations, etc. Form a hypothesis on how the object of interest works. Determine the observable consequences of your idea, using reasonable assumptions and well-established “laws.” Formulate experiments to see if the predicted consequences happen. Outline of Scientific Method:  Outline of Scientific Method If the new observations agree with the predictions: great, keep going. If the new observations don’t agree with the predictions: start over! Messy Details:  Messy Details Observations are never exact: they have measurement uncertainties x = 3.0 +/- 0.5 kg usually means “there is a 68% chance that the true answer is between 2.5 and 3.5 kg.” Sometimes there are mistakes or fraud. Try to get more data or better data. Messy Details:  Messy Details Sometimes two different hypotheses make basically the same predictions about the outcome of a given experiment. Think up experiments where the two predicted outcomes are different. A Good Recap From Nick Strobel:  A Good Recap From Nick Strobel http://www.astronomynotes.com/scimethd/s1.htm Carl Sagan’s Guide to Skeptical Thinking:  Carl Sagan’s Guide to Skeptical Thinking Carl Sagan’s Guide to Skeptical Thinking:  Carl Sagan’s Guide to Skeptical Thinking Whenever possible, there must be independent confirmation of the “facts.” Carl Sagan’s Guide to Skeptical Thinking:  Carl Sagan’s Guide to Skeptical Thinking Whenever possible, there must be independent confirmation of the “facts.” Experiments must be repeatable. Carl Sagan’s Guide to Skeptical Thinking:  Carl Sagan’s Guide to Skeptical Thinking Whenever possible, there must be independent confirmation of the “facts.” Experiments must be repeatable. Encourage debate, get other opinions. Carl Sagan’s Guide to Skeptical Thinking:  Carl Sagan’s Guide to Skeptical Thinking Whenever possible, there must be independent confirmation of the “facts.” Experiments must be repeatable. Encourage debate, get other opinions. Think up more than one hypothesis, think of tests to disprove them. Carl Sagan’s Guide to Skeptical Thinking:  Carl Sagan’s Guide to Skeptical Thinking Don’t get too attached to an idea because it is “yours.” Be willing to start over if your ideas do not hold up. Carl Sagan’s Guide to Skeptical Thinking:  Carl Sagan’s Guide to Skeptical Thinking Don’t get too attached to an idea because it is “yours.” Be willing to start over if your ideas do not hold up. Quantify predictions to the extent possible (don’t be vauge). Carl Sagan’s Guide to Skeptical Thinking:  Carl Sagan’s Guide to Skeptical Thinking Don’t get too attached to an idea because it is “yours.” Be willing to start over if your ideas do not hold up. Quantify predictions to the extent possible (don’t be vauge). If there is a chain of arguments, every link must work. Carl Sagan’s Guide to Skeptical Thinking:  Carl Sagan’s Guide to Skeptical Thinking Ask if the hypothesis can be proven wrong. Ideas that are untestable or unfalsifiable are not worth too much. Carl Sagan’s Guide to Skeptical Thinking:  Carl Sagan’s Guide to Skeptical Thinking Ask if the hypothesis can be proven wrong. Ideas that are untestable or unfalsifiable are not worth too much. Control experiments are essential. For example, if it is claimed that a new pill cures an illness 20% of the time, we should check to see if the spontaneous remission rate is not 20%. Carl Sagan’s Guide to Skeptical Thinking:  Carl Sagan’s Guide to Skeptical Thinking Separate the variables. For example, taking an aspirin and a nap cures my headaches after two hours. Did the aspirin alone cure the headache? Was it the nap? None of the above? Carl Sagan’s Guide to Skeptical Thinking:  Carl Sagan’s Guide to Skeptical Thinking “Double Blind” studies are also essential since study subjects and researchers may influence the outcome (either knowing or unknowingly). The patient and the doctor do not know who got the experimental drug and who got the placebo. What NOT to do:  What NOT to do What NOT to do:  What NOT to do Ad hominem: attack the arguer and not the argument. What NOT to do:  What NOT to do Ad hominem: attack the arguer and not the argument. Argument by authority. What NOT to do:  What NOT to do Ad hominem: attack the arguer and not the argument. Argument by authority. Argument from adverse consequences. What NOT to do:  What NOT to do Ad hominem: attack the arguer and not the argument. Argument by authority. Argument from adverse consequences. Absence of evidence is not evidence of absence. What NOT to do:  What NOT to do Begging the question or assuming the answer. “We must have the death penalty to discourage violent crime.” What NOT to do:  What NOT to do Begging the question or assuming the answer. “We must have the death penalty to discourage violent crime.” Observational selection, or counting the hits and ignoring the misses. What NOT to do:  What NOT to do Begging the question or assuming the answer. “We must have the death penalty to discourage violent crime.” Observational selection, or counting the hits and ignoring the misses. Misunderstanding or misusing statistics. What NOT to do:  What NOT to do Excluded middle or false dichotomy. “If you’re not part of the solution, you are part of the problem.” What NOT to do:  What NOT to do Excluded middle or false dichotomy. “If you’re not part of the solution, you are part of the problem.” What NOT to do:  What NOT to do Excluded middle or false dichotomy. “If you’re not part of the solution, you are part of the problem.” Straw man “You care more about the spotted owl than about people.” Next::  Next: The Sky The Clockwork of the Universe:  The Clockwork of the Universe There are many familiar astronomical cycles: The Day/Night cycle. The phases of the Moon (the lunar cycle). The seasons of the year. The seven day week??? Pop Quiz:  Pop Quiz What is the shape of the Earth? The Earth:  The Earth How do we know the Earth is spherical? The Earth:  The Earth How do we know the Earth is spherical? Curved shadow of the Earth on Moon during eclipse The manner in which ships at sea disappear when they sail away The fact that as you go north-south certain stars disappear Constellations:  Constellations People have long made up stories about groups of stars that appear close together on the sky. Such groupings are called constellations. The sky was “officially” divided up into 88 constellations in 1930 so that a star is associated with only one constellation. Constellations:  Constellations The modern constellations have strictly defined boundaries by international agreement. Constellations:  Constellations Many constellation names are derived from characters in Greek or Roman mythology. Here is Cassiopeia, with its distinctive “W”. The stars are usually not physically associated with each other. Constellations:  Constellations Here is the :Big Dipper”, which is not an “official” constellation but part of a larger one. Again, the stars are usually not physically associated with each other. Constellations:  Constellations Taurus the Bull (left) and Orion the hunter (right) appear in the winter sky. Stellar Brightness: Magnitudes:  Stellar Brightness: Magnitudes Historically (e.g. Hipparcos in the First Century), the brightness of stars as seen by the eye have been measured on a magnitude scale: The brightest stars were “first magnitude”. The faintest stars were “sixth magnitude”. Brighter objects have smaller magnitudes. Stellar Brightness: Magnitudes:  Stellar Brightness: Magnitudes In modern times, it was discovered that the human eye has a nonlinear response to light: if one source of light has twice the light as a second source, then the first source would not appear by eye to be twice as bright. The response of the eye is logarithmic, so that differences of magnitudes correspond to ratios of brightness. The Magnitude Scale:  The Magnitude Scale The modern of the magnitude scale is set up so that a difference of 5 magnitudes corresponds to a ratio of brightnesses of 100. Bright objects can have negative apparent magnitudes. The Celestial Sphere:  The Celestial Sphere Imagine the sky as a hollow sphere with the stars attached to it. This sphere rotates once every 24 hours. This imaginary sphere is called the celestial sphere. Even though we know it is not the case, it is useful to imagine the Earth as being stationary while the celestial sphere rotates around it. The Celestial Sphere:  The Celestial Sphere The north celestial pole is directly above the north pole on the Earth. The south celestial pole is directly above the south pole on the Earth. The celestial equator is an extension of the Earth’s equator on the sky. The zenith is the point directly over your head. The horizon is the circle 90 degrees from the zenith. The Celestial Sphere:  The Celestial Sphere The celestial poles and the celestial equator are the same for everyone. The zenith and the horizon depend on where you stand. http://www.astronomynotes.com/nakedeye/s4.htm Stellar Coordinates and Precession:  Stellar Coordinates and Precession There are a few ways to specify the location of a star (or planet) on the sky: Altitude/Azimuth: The altitude describes how many degrees the star is above the horizon, the azimuth describes how far the star is in the east-west direction from north. The altitude and azimuth of a star is constantly changing owing to the motion of the star on the sky! Stellar Coordinates and Precession:  Stellar Coordinates and Precession There are a few ways to specify the location of a star (or planet) on the sky: Equatorial system: Lines of longitude on the earth become right ascension, measured in units of time. The RA increases in the easterly direction. Lines on latitude on the earth become declination, measured in units of degrees. DEC=90o at the north celestial pole, 0o at the equator, and -90o at the south celestial pole. http://www.astronomynotes.com/nakedeye/s6.htm The Clockwork of the Universe:  The Clockwork of the Universe

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