United States Solar Eclipse of 2017 21 Aug 21 August 2017 Total Solar Eclipse Interactive 2017 Eclipse Google Map Course Announcements Quiz 1 on Wednesday 31 August Hints today and in coming lectures You should be registered for Mastering Astronomy by now The first assignment is now past due Course ID LINDSAYA152F2016 Friday 2 Sept class cancelled Assignments Reading Assignments Chapter 2 Sections 2 1 2 4 Read by Wednesday 31 August Parallel Lectures No new episodes Mastering Astronomy Chapter 1 Homework Due Wednesday 31 Aug at 11 59 PM EDT Quiz 1 Hints A few types of questions to expect 3 Challenge question If the Earth were to orbit the Sun twice as fast as it currently does then the Solar Day would A Become Longer B Become Shorter C Stay the Same Possible variants Same question but asked about the Sidereal Day The Earth orbits slower rather than faster General hints Given a number be able to write it out in scientific notation Be able to know quantity is bigger smaller if given it using our metric system prefixes e g What is bigger 13 8 Gyr or 13 8 Myr Quiz 1 Possible Questions 1 For a Total Solar Eclipse to occur the Moon must be in what phase New Moon For the Moon to cast it s shadow on the Earth it must be between the Sun and Earth 2 For a Total Lunar Eclipse to occur the Moon must be in what phase Full Moon For the Earth to cast it s shadow on the Moon it must be between the Sun and Moon Incoming Sunlight 4 Weeks Day 0 New 2 Weeks Later Full 1 Week Later Quarter Measuring Distances Simple Geometry and Trigonometry Distance Triangulation 90o Baseline Can calculate Distance to Object given that you have measured 1 the Baseline distance and 2 the angle You won t have to work out the geometry trigonometry but do know the method Angular Measurement In Astronomy things are very far away so angles are typically very small Full circle contains 360 degrees Each degree contains 60 arcminutes Each arc minute contains 60 arc seconds Angular size measured in degrees arcmin and arcsec of an object depends on its actual size and distance from viewer For an example of angular size think about sitting in the front row of a movie theater versus the back row Angular Measure Astronomical Example The Hubble eXtreme Deep Field XDF 2 4 arcmin x 2 4 arcmin Contains approximately 10 000 galaxies 1 million seconds of exposure time 11 5 days This angular size is roughly the equivalent to the patch of sky covered by a penny that is held 100 feet away from you 2 4 Angular Measure HUDF compared to the Moon 0 5o 30 1 800 Illustration Credit NASA ESA and Z Levay STScI Moon Image Credit T Rector I Dell Antonio NOAO AURA NSF Approximate Angular Sizes Your cheat sheet to estimating angular size 5o 1o 10o 25o 15o 1 arcsec 4 km Image Credit NASA CXC M Weiss Measuring Distances Astronomy Method Parallax Parallax Same principle as Triangulation BUT here we measure the angle via the apparent motion of an object against a distant background using TWO different vantage points A and B in diagram Baseline One point on Earth to another point on Earth Local Cosmic Distances Fundamental Astronomy Concept Alert Parallax is the apparent displacement change in position a distant object has when observed from two different points Measured in angular distance radians degrees arcminutes arcseconds B DISTANCE 2 1B 1 2 2B 2A 1A Fixed Background Baseline Distance A DISTANCE 1 Local Cosmic Distances Useful only for nearest stars and Solar System objects Parallax is inversely proportional to distance i e if distance increases then parallax decreases Extremely hard to measure for small angles Angle increases with increasing baseline B DISTANCE 2 1B 1 2 2B 2A 1A Fixed Background Baseline Distance A DISTANCE 1 Local Cosmic Distances Formalizing the definition of parallax Here half of the angular displacement is defined as the parallactic angle usually referred to simply as the parallax Baseline Distance A B Parallactic Angle 2 2A Fixed Background Distance to Planet Our largest baseline Earth s orbit Distance 1 AU or Planet or Solar System Body Using the measured parallax with Earth s orbit as the baseline baseline distance 1 AU is how astronomers determine the distance to nearby stars 1 AU Using Distance to Measure Size With known distance we can measure size of planets The angular diameter is just a proportion of a circle 2 x Distance is just circumference of planet s orbit Our basic method to measure the diameters of planets Distance and Size Take Away Points We can measure the distances to the planets using parallax Once the distance is known we can measure the angular size of a planet to determine it s true size diameter or radius Diameter is size of spherical object Radius is half the diameter or center of object to surface distance Science A few generalities Science is a system of knowing that provides explanations for HOW not why natural phenomena Credit Randall Monroe and the universe work The sciences are NOT in the business of proving things We are in the business of providing explanations that Are testable with clear hypotheses predictions Are falsifiable even by a single new piece of evidence Are repeatable Rely upon evidence data and are flexible in the light of new evidence gathered by observations experimentation and modeling Provide a high level of confidence with their predictions and results Scientific Theory Not the colloquial use of the word theory It s just a theory Qualities of a Scientific Theory Must be testable Must be continually tested Should be simple Should be elegant Scientific theories can be proven wrong Falsifiability More so they can never be proven right with 100 percent certainty Scientists We aren t in the business of proving things Scientific Theory and Methods Science A system of knowing Let s start with some limited observations of a natural phenomenon Recording those observations whether that be descriptive or numerical is our initial evidence or data This evidence allows for the formation of a hypothesis attempting to explain some aspect of that phenomenon A hypothesis is a predicted outcome that can be tested via further observation and experimentation Scientific Theory and Methods Science A system of knowing What do we do with a hypothesis Design and perform further experiments to test the predicted outcome If the prediction is fulfilled within confidence bounds then we have gained some knowledge albeit limited about a natural phenomenon Confirmation or rejection of hypothesis leads to
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