Astronomy 101 The Solar System Tuesday, Thursday 2:30-3:45 pm Hasbrouck 20 Tom Burbine [email protected] CourseOffice HoursHomeworkAstronomy InformationFinalHW #9HW #10Exam #232 Extrasolar planets were just announcedRadioactive DecaySlide Number 12Slide Number 13Slide Number 14What are the assumptions to get an age?What are the assumptions?Basic FormulaSlide Number 18How do you determine isotopic values?How do you determine isotopic values?It is easierExampleExampleSlide Number 24Slide Number 25Carbon-14Slide Number 27Slide Number 28Slide Number 29Why is Carbon-14 still present if it has such a short half-life? Why is Carbon-14 still present if it has such a short half-life? Slide Number 32Composition of the PlanetsDifferent bodies have different densitiesLife of a StarSlide Number 36CondensingProtostarSlide Number 39When does a protostar become a starSlide Number 41Formation of Solar SystemCompositionSlide Number 44Slide Number 45Slide Number 46Slide Number 47Slide Number 48Slide Number 49Slide Number 50Slide Number 51Slide Number 52Any Questions?Astronomy 101The Solar SystemTuesday, Thursday2:30-3:45 pmHasbrouck 20Tom [email protected]• Course Website:– http://blogs.umass.edu/astron101-tburbine/• Textbook:– Pathways to Astronomy (2nd Edition) by Stephen Schneider and Thomas Arny.•You also will need a calculator.Office Hours• Mine• Tuesday, Thursday - 1:15-2:15pm•Lederle Graduate Research Tower C 632• Neil• Tuesday, Thursday - 11 am-noon • Lederle Graduate Research Tower B 619-OHomework• We will use Spark•https://spark.oit.umass.edu/webct/logonDisplay.dowebct• Homework will be due approximately twice a weekAstronomy Information• Astronomy Help Desk• Mon-Thurs 7-9pm• Hasbrouck 205•The Observatory should be open on clear Thursdays • Students should check the observatory website at: http://www.astro.umass.edu/~orchardhillfor updated information• There's a map to the observatory on the website.Final• Monday - 12/14 • 4:00 pm• Hasbrouck 20HW #9• Due todayHW #10• Due Oct. 29Exam #2• Average was a 75• Grades from 100s to a 27.5• http://web.mit.edu/thb/www/exam2a.answers.doc• Average (80% exams, 20% HW) for people who took both exams is ~8132 Extrasolar planets were just announcedThe new alien planets, which bring the known count beyond 400, were found with the HARPS spectrograph on the European Southern Observatory's 3.6-m telescope in La Silla, Chile.Some just five times the mass of Earth Others five times heftier than giant Jupiterhttp://www.msnbc.msn.com/id/33379852/ns/technology_and_science-space/Radioactive Decayhttp://academic.brooklyn.cuny.edu/geology/leveson/core/topics/time/graphics/radio1.gifWhat are the assumptions to get an age?What are the assumptions?• No loss of parent atoms– Loss will increase the apparent age of the sample. • No loss of daughter atoms– Loss will decrease the apparent age of the sample. • No addition of daughter atoms or if daughter atoms was present when the sample formed– If there was, the age of the sample will be inflated• These can possibly be all corrected forBasic Formula• Number of daughter atoms formed = number of parent atoms consumed• If there were daughter atoms originally there• D – Do= no- n• Remember: n = noe-λtso no = n eλt• D- Do = n eλt– n•D = Do + n (eλt– 1)Commonly Used Long-Lived Isotopes in GeochronologyRadioactiveParent (P)RadiogenicDaughter (D)StableReference (S)Half-life, t½(109y)Decay constant, l(y-1)40K 40Ar 36Ar 1.25 0.58x10-1087Rb 87Sr 86Sr 48.8 1.42x10-11147Sm 143Nd 144Nd 106 6.54x10-12232Th 208Pb 204Pb 14.01 4.95x10-11235U 207Pb 204Pb 0.704 9.85x10-10238U 206Pb 204Pb 4.468 1.55x10-10How do you determine isotopic values?How do you determine isotopic values?• Mass SpectrometerIt is easier• To determine ratios of isotopic values than actual abundancesExample•87Rb →87Sr + electron + antineutrino + energy• Half-life is 48.8 billion years•87Sr = 87Srinitial + 87Rb (eλt– 1)• Divide by stable isotope•87Sr = 87Srinitial + 87Rb (eλt– 1)86Sr 86Sr 86SrExample• Formula for line•87Sr = 87Srinitial + (eλt– 1)87Rb86Sr 86Sr 86Sry = b + m xhttp://www.asa3.org/aSA/resources/wiens2002_images/wiensFig4.gif= (eλt– 1)Carbon-14• 99% of the carbon is Carbon-12• 1% is Carbon-13• 0.0000000001% is Carbon-14• The half-life of carbon-14 is 5730±40 years. • It decays into nitrogen-14 through beta-decay (electron and an anti-neutrino are emitted).• Due to Carbon-14’s short half-life, can only date objects up to 60,000 years old• Plants take up atmospheric carbon through photosynthesishttp://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/cardat.html• When something dies, it stops being equilibrium with the atmosphere http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/cardat.htmlWhy is Carbon-14 still present if it has such a short half-life?Why is Carbon-14 still present if it has such a short half-life?• Cosmic rays impact Nitrogen-14 and create Carbon-14• Cosmic rays are energetic particles (90% are protons) originating from space. From the Sun (solar cosmic rays) or outside the solar system (galactic cosmic rays)• n + 14N → 14C + p• http://en.wikipedia.org/wiki/Image:Radiocarbon_bomb_spike.svgComposition of the PlanetsDifferent bodies have different densities• Density = Mass/Volume• M = 4π2d3/GP2V =4/3πR3Life of a Star• A star-forming cloud is called a molecular cloud because low temperatures allow Hydrogen to form Hydrogen molecules (H2)• Temperatures like 10-50 KRegion is approximately 50 light years acrossCondensing• Interstellar clouds tends to be lumpy• These lumps tend to condense into stars• That is why stars tend to be found in clustersProtostar• The dense cloud fragment gets hotter as it contracts• The cloud becomes denser and radiation cannot escape• The thermal pressure and gas temperature start to rise and rise•The dense cloud fragment becomes a protostarWhen does a protostar become a star• When the core temperatures reaches 10 million K, hydrogen fusion can start occurringFormation of Solar System• Solar Nebula Theory (18thcentury) – Solar System originated from a rotating, disk-shaped cloud of gas and dust• Modern theory is that the Solar System was born from an interstellar cloud (an enormous rotating cloud of gas and dust)Composition• ~71% is Hydrogen• ~27% is Helium• ~2% are other
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