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MIT AST 101 - Lecture Slides

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Astronomy 101 The Solar System Tuesday, Thursday 2:30-3:45 pm Hasbrouck 20 Tom Burbine [email protected] HoursHomeworkAstronomy InformationFinalHW #7HW #8HW #9Exam #2Formulas you need to knowMore FormulasLCROSS ImpactSolar SystemSunSlide 16MercuryVenusEarthEarth’s crustMoonCometMarsSlide 24AsteroidSlide 26http://spaceguard.esa.intSlide 28JupiterSlide 30IoEuropaSaturnSlide 34UranusNeptunePlutoSlide 38How do we determine what astronomical bodies are made of?Slide 40Slide 41Planetary densitiesUse Newton’s Laws of motion…But we want to know the mass of a planet!Slide 45VolumeDensity = ρ = Mass/Volume ρEarth = 5.515 g/cm3Density of waterSlide 49Slide 50Slide 51Slide 52Slide 53How big is the Solar System? One boundaryWhat is out there?Slide 56Another possible boundary- HeliopauseSlide 58Slide 59Slide 60Slide 61To learn how the Solar System formedWhat’s the difference?Slide 64How do we know the age of the solar systemRadioactive datingWhat do we date?MeteoritesHow old is the solar system?Slide 70AgesHow do you determine this age?Dating a planetary surfaceRadioactivitySlide 75Half-LifeRadioactive DatingSlide 78Slide 79Slide 80Any 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/~orchardhill for updated information•There's a map to the observatory on the website.Final•Monday - 12/14 •4:00 pm•Hasbrouck 20HW #7•Due todayHW #8•Due todayHW #9•Due October 27Exam #2•Next Thursday•Bring a calculator and a pencil•No cell phones, Blackberries, iPhones•Covers material from September 22 through October 8 (Units 14-31)Formulas you need to know•F = GMm/r2•F = ma•a = GM/r2•Escape velocity = sqrt(2GM/r)•T (K) = T (oC) + 273.15•c = f*•E = h*f•KE = 1/2mv2•E = mc2More Formulas•Power emitted per unit surface area = σT4•λmax (nm) = (2,900,000 nm*K)/T•Apparent brightness = Luminosity 4 x (distance)2LCROSS Impact•http://www.youtube.com/watch?v=VVYKjR1sJY4•http://dsc.discovery.com/videos/news-lcross-smashes-into-the-moon.htmlSolar System•Sun•Eight Planets•Their moons•Dwarf Planets•Asteroids•CometsSunSun•74% H•25% He•Traces of everything elseMercuryVenusEarthEarth’s crust•46.6% O•27.7% Si•8.1% Al •5.0% Fe •3.6% Ca•2.8% Na•2.6% K •2.1% MgMoonCometMarsAsteroidhttp://spaceguard.esa.intHiroshimaMeteoriteschondritePallasite – mixtures of olivine and metalIronJupiterJupiter•90% H•10% He•Traces of everything elseIoEuropaSaturnSaturn•75% H•25% He•Traces of everything elseUranusNeptunePlutoHow do we determine what astronomical bodies are made of?How do we determine what astronomical bodies are made of?•Measure how they emit or reflect light–Tells you about their surfaces•Measure their physical properties–Tells you about their interiorsPlanetary densitiesvolumeweightdensity 334rvolumeBut how do we determine mass?massUnits are g/cm3 or kg/m31 g/cm3 = 1,000 kg/m3Use Newton’s Laws of motion…2324paGMWhere P is the period of a planet’s orbita is the distance from the planet to the SunG is Newton’s constantM is the mass of the SunThis assumes that orbits are circles, and that the mass of a planet is tiny compared to the mass of the Sun.Use this relation with P and a for the Earth, and you’ll get the mass of the Sun: MSun = 1.98892 x 1030 kgBut we want to know the mass of a planet!Where F is the gravitational forceG is the constant of proportionalityM and m are the two masses exerting forcesr is the radius of the planeta is its acceleration due to gravity2rGmMF and F = mamarGmMF 2arGM2Solve for M, the mass of the Earth, by usinga = 9.8 m/sec2r = 6.4 x 106 mG = 6.67 x 10-11 m3/(kg sec2)GarM2Re-arrange to getMEarth = 5.9736 x 1024 kgVEarth = 1.0832 x 1021 m3DEarth = 5515 kg/m3 = 5.515 g/cm3Volume•If you assume a planet is a sphere:•Volume = 4/3πr3Density = ρ = Mass/VolumeρEarth = 5.515 g/cm3Density (g/cm3)Metallic iron 7.87Basalt 3.3Water 1.0Water Ice 0.9Liquid Hydrogen 0.07Density of water•Density of water is 1 g/cm3•Density of water is 1,000 kg/m3Density (g/cm3)Iron 7.87Basalt 3.3Water 1.0Cold ices 0.07-0.09DensityWhat do these densities tell us?How big is the Solar System?One boundary•Some scientists think that the furthest influence of the Solar System extends out to 125,000 astronomical units (2 light years). •Since the nearest star is 4.22 light-years away, the Solar System size could extend almost half-way to the nearest star.•Astronomers think that the Sun's gravitational field dominates the gravitational forces of the other stars in the Solar System out to this distance.What is out there?•The Oort Cloud (the source of long period comets) extends out to a distance of 50,000 AU, and maybe even out to 100,000 AU. •The Oort Cloud has never been seen directly. •Appears to exist because comets with extremely long orbits sometimes pass near the Sun and then head back out again. •The Oort cloud could have a trillion icy objects.Another possible boundary- Heliopause•Heliopause is the region of space where the sun's solar wind meets the interstellar medium. Solar wind's strength is no longer great enough to push back against the interstellar medium.–Solar wind – charged particles ejected from the Sun–Interstellar medium – gas and dust between stars•Heliosphere is a bubble in space "blown" into the interstellar medium•It is a fluctuating boundary that is estimated to be ~80-100 AU away•Termination shock - the point where the solar wind slows down.•Bow shock - the point where the interstellar medium, travelling in the opposite direction, slows down as it collides with the heliosphere.To learn how the Solar System


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MIT AST 101 - Lecture Slides

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