Astronomy 100 Tuesday, Thursday 2:30 - 3:45 pm Tom Burbine [email protected] www.xanga.com/astronomy100Two thing about the tests and the final What was easiest question on the 2nd exam?Was this the easiest question on 2nd exam?E = mc2Who came up with it?How many people got this question wrong?33 about 10% of the classWhat was the easiest question on the 1st exam?Was this the easiest question on 1st exam?Milky Way GalaxyHow many people got this question wrong?12 about 4% of the classFinals1st Homework question (March 24) (beginning of class)NeutrinosWhat is the solar neutrino problem?What is the solar neutrino problem?How was the Homestake Gold Mine used to detect neutrinos?2nd HW question (due March 24th) (beginning of class)I know this HW was difficultSo Things you need to knowAndAndCalculationCalculationFusionWhat is happening to the amount of Helium in the Sun?What is happening to the amount of Helium in the Sun?HW (Chapter 16)So how does the Sun stay relatively constant in Luminosity (power output)Parts of Sun CoreRadiation zonePhotons emitted from Fusion reactionsConvection ZonePhotosphereSunspotsSunspotsSunspot CycleMaunder MinimumAtmosphere of the SunAtmosphere of the SunCoronaPRS for making it through classQuestionsAstronomy 100Tuesday, Thursday 2:30 - 3:45 pmTom [email protected]/astronomy100Two thing about the tests and the finalWhat was easiest question on the 2ndexam?Was this the easiest question on 2ndexam?• Who was the first to propose the formula E=mc2for converting matter into energy?• A) Isaac Newton• B) Albert Einstein• C) Stephen Hawking• D) Richard Feynman• E) Johannes KeplerE = mc2• m is mass in kilograms• c is speed of light in meters/s• So E is in joules• very small amounts of mass may be converted into a very large amount of energy andWho came up with it?How many people got this question wrong?33about 10% of the classWhat was the easiest question on the 1st exam?Was this the easiest question on 1st exam?• What galaxy do we reside in? • A) Andromeda • B) Milky Way• C) ecliptic • D) Sirius • E) Ursa MajorMilky Way Galaxy• Milky Way is 100,000 light years in diameter• There are ~100 billion stars in the Milky WayHow many people got this question wrong?12about 4% of the classFinals• The Final exams will be questions from the first 4 exams with the numbers changed1st Homework question (March 24)(beginning of class)• I want you to detail the hydrogen fusion reaction (Steps 1 through 3) with words (written by hand) and pictures• What is the solar neutrino problem?• How was the Homestake Gold Mine used to detect neutrinos?Figure 15.72 protons fuse togetherForms proton and neutron(deuterium- Hydrogen isotope)Positron given offand destroyed by collidingwith electron2 gamma rays given offNeutrino given offPositron-positively chargedelectronFigure 15.7proton fuses with deuterium Forms Helium-3Gamma ray given offFigure 15.7Collision of two Helium-3nucleusProduces Helium-4 nucleus and 2 protonsSteps 1 and 2 must occur twiceNeutrinos• Neutrinos – almost massless particles•No charge• It takes a neutrino 2 seconds to exit the SunWhat is the solar neutrino problem?• A) More neutrinos appear to be produced from the Sun than expected from models• B) Less neutrinos appear to be produced from the Sun than expected from models• C) Neutrinos are dangerous to humans• D) Neutrinos interfere with the fusion of hydrogen into helium• E) Neutrinos turn helium into LithiumWhat is the solar neutrino problem?• A) More neutrinos appear to be produced from the Sun than expected from models• B) Less neutrinos appear to be produced from the Sun than expected from models• C) Neutrinos are dangerous to humans• D) Neutrinos interfere with the fusion of hydrogen into helium• E) Neutrinos turn Helium into LithiumHow was the Homestake Gold Mine used to detect neutrinos?• A 400,000 liter vat of chlorine-containing cleaning fluid was placed in the Homestake gold mine• Every so often Chlorine would capture a neutrino and turn into radioactive argon• Modelers predict 1 reaction per day• Experiments found 1 reaction every 3 days2ndHW question (due March 24th)(beginning of class)• How much longer will it take the Sun to use up all its “fuel”?• When the Sun uses up its fuel it will start expanding, which will be bad for people living on Earth• I want an answer in years• Show your workI know this HW was difficult• This homework is to show how you can make rough estimates • Know 10% of sun can undergo fusion• Know 0.7% mass during fusion reaction is turned into energy• Determine lifetime of SunSo • You get 1 point for turning it in• You get 1 point for getting right answerThings you need to know• Energy source for sun is four hydrogen atoms combining to produce one helium atom • about 0.7% of the original mass is turned into energy during this process• 10% of the Sun’s mass is hot enough to undergo fusion• Mass of the Sun = 2 x 1030 kgAnd• Total lifetime = (energy available) (rate [energy/time] at which sun emits energy)• rate [energy/time] at which the Sun emits energy is equal to 3.8 x 1026Watts (Joules/second)And• Time left = Lifetime – current age• Current age = ~5 billion yearsCalculation• Mass of the Sun that is turned into energy• m = 2 x 1030 kg times 10% times 0.7%• m = 1.4 x 1027 kg of Sun can be turned into energy• E = mc2• E = 1.4 x 1027 kg times 9 x 1016 m2/s2• E = 1.26 x 1044 JoulesCalculation• Lifetime = 1.26 x 1044 Joules/3.8 x 1026Joules/second• Lifetime = 3.3 x 1017 seconds• Lifetime = 1.05 x 1010years• Time left = 10.5 billion years – 5 billion years• Time left = 5.5 billion yearsFusion• The rate of nuclear fusion is a function of temperature• Hotter temperature – higher fusion rate• Lower temperature – lower fusion rate• If the Sun gets hotter or colder, it may not be good for life on EarthWhat is happening to the amount of Helium in the Sun?• A) Its increasing• B) its decreasing• C) Its staying the sameWhat is happening to the amount of Helium in the Sun?• A) Its increasing• B) its decreasing• C) Its staying the sameHW (Chapter 16)• I want you to draw me a Hertzsprung-Russell Diagram• Label the axes• Label the regions with different types of stars• O, B A, F, G, K, M• Tell me the phrase people use to remember the orderSo how does the Sun stay relatively constant