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ASTR 1200 Announcements Exam #1 in class, next Tuesday, October 7 Have posted review sheet and sample exam Help room: Mondays 3-5,Duane G2B90 Review Today Josh review/help session today after class? Website http://casa.colorado.edu/~wcash/APS1200/APS1200.html Structure of the Exam Closed book. Calculators strongly recommended. (Check batteries!) Pencils are a good idea for the calculations. (but not necessary) Formulae and constants you need will be provided. Just like the sample exam. Will not be a test of time. Should be finished in under one hour. But will have full 75minutes to complete it. How to Study Knowledge Facts. Multiple Choice Fast. Do these first. Conceptual How things work. Written Answers Calculations Identify and use the formulas. These take longer. Do them last. Homeworks Redo them. Do additional exercises. Lecture Notes Go through each powerpoint slide and make certain you understand. Textbook Background reading of for explanation of individual points. Test yourself to identify weak areas using review sheet and sample exam. Material Covered Drakes Equation and prevalence of Life in the Universe Scientific Notation Sizes of things Formation of Solar System Position, velocity, acceleration Newton’s Laws Orbits Escape Velocity Surface Gravity Orbital Period Structure of Sun Nuclear Processes Solar Activity Material Covered Our place in the galaxy Light years and parsecs Parallax Proper Motion Brightness Magnitudes and Absolute Magnitudes Concept only from here on: Electromagnetic Spectrum and its parts Spectroscopy Spectral Types The Spectral Types Stars of Orion's Belt >30,000 K Lines of ionized helium, weak hydrogen lines <97 nm (ultraviolet)* B Rigel 30,000 K10,000 K Lines of neutral helium, moderate hydrogen lines 97-290 nm (ultraviolet)* A Sirius 10,000 K-7,500 K Very strong hydrogen lines 290-390 nm (violet)* F Polaris 7,500 K6,000 K Moderate hydrogen lines, moderate lines of ionized calcium 390-480 nm (blue)* G Sun, Alpha Centauri A 6,000 K5,000 K Weak hydrogen lines, strong lines of ionized calcium 480-580 nm (yellow) K Arcturus 5,000 K3,500 K Lines of neutral and singly ionized metals, some molecules 580-830 nm (red) M Betelgeuse, Proxima Centauri <3,500 K Molecular lines strong >830 nm (infrared) O *All stars above 6,000 K look more or less white to the human eye because they emit plenty of radiation at all visible wavelengths. The H-R Diagram Plot of Brightness vs Temperature -5 Giants Rigel Capella Brightness 0 Sirius Procyon Sun +5 Main Sequence a Cen B White Dwarfs +10 Sirius B Prox Cen +15 O B A F G Spectral Type K M The H-R Diagram The Main Sequence Stars Differ By: Mass Age Composition Nothing else! And composition doesn’t vary Age and Mass only. Those on main sequence are all burning H so age drops out. MS is function of MASS only!!! Full, Artistic H-R As mass of MS star increases, both R and T increase increasing size sAT4 T constant on any vertical line Newly Formed Star -5 Giants Rigel Capella 0 M Sirius Protostar Procyon Sun +5 Main Sequence Then sits while burning H a Cen B White Dwarfs +10 Sirius B Prox Cen +15 O B A F G Spectral Type K Large, Low T. Settles down to MS M MS Lifetime What determines amount of time a star stays on Main Sequence? Just like a kerosene heater: Amount of fuel and rate of burn. More Mass = More Fuel More Luminosity = Greater Burn Rate We can scale from the Sun: M = 1M L = 1L Sun lasts 1010 years M MSLife 10 L 10 M in solar masses L in solar luminosities Some Lifetimes Sun Sirius Prox Cen Rigel Mass Luminosity Lifetime in Billion Years 1 2 .4 8 1 10 .001 10,000 10 2 4000 .008 Dinky little stars like Prox Cen will last trillions of years Huge stars like Rigel are gone in a few million There aren’t many large stars out there, because they don’t last. 10,000 O stars of the 100,000,000,000 Milky Way stars