天文学概论2宇宙概观课件.ppt

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1、天文学概论教师：马素丽第一章 宇宙概观 1.1 太阳系1.2 恒星世界1.3 银河系及河外星系 1.1.1 太阳1.1.2 太阳系行星1.1.3 地球1.1.4 日月食1.1.5 太阳系的物质分布1.11.1.1 太阳 Apparent surface layer of the sun光球（photosphere）日冕 Depth 500 km Temperature 5800 oK Highly opaque(H-ions)Absorbs and re-emits radiation produced in the solar interior光球的能力传输Energy generated

2、in the suns center must be transported outward.In the photosphere,this happens through对流（Convection）Bubbles of hot gas rising upCool gas sinking down 1000 kmBubbles last for 10 20 min.米粒组织（Granulation）is the visible consequence of convection针状体Spicules:Filaments of cooler gas from the photosphere,ri

3、sing up into the chromosphere.Visible in H a emission.Each one lasting about 5 15 min.太阳大气层VisiblePhotosphereUltravioletChromosphereCoronal activity,seen in visible lightCoronaSun Spot Regions太阳风（the Solar Atmosphere）Constant flow of particles from the sun.Velocity 300 800 km/s Sun is constantly los

4、ing mass:107 tons/year(10-14 of its mass per year)太阳黑子（Sun Spots）Cooler regions of the photosphere(T 4240 K).Only appear dark against the bright sun.Would still be brighter than the full moon when placed on the night sky!太阳黑子（2）Active RegionsVisibleUltraviolet黑子中的磁场（Magnetic Fields in Sun Spots）Magn

5、etic fields on the photosphere can be measured through the Zeeman effect Sun Spots are related to magnetic activity on the photosphere太阳黑子(3)Magnetic field in sun spots is about 1000 times stronger than average.In sun spots,magnetic field lines emerge out of the photosphere.MagneticNorthPolesMagneti

6、cSouthPoles磁力线（Magnetic Field Lines）Magnetic North PoleMagnetic South PoleMagnetic Field Lines恒星黑子（Star Spots）?Other stars might also have sun spot activity:Image constructed from changing Doppler shift measurements太阳周（The Solar Cycle）11-year cycleReversal of magnetic polarityAfter 11 years,North/So

7、uth order of leading/trailing sun spots is reversed=Total solar cycle=22 years太阳磁动力学（Magnetic Dynamo）This differential rotation might be responsible for magnetic activity of the sun.The sun rotates faster at the equator than near the poles.磁环（Magnetic Loops）Magnetic field lines太阳磁活动周（Magnetic Cycle）

8、After 11 years,the magnetic field pattern becomes so complex that the field structure is re-arranged.New magnetic field structure is similar to the original one,but reversed!New 11-year cycle starts with reversed magnetic-field orientation其他恒星上的磁活动周（Magnetic Cycles on Other Stars）H and K line emissi

9、on of ionized Calcium indicate magnetic activity also on other stars.日珥（Prominences）Looped Prominences:gas ejected from the suns photosphere,flowing along magnetic loopsRelatively cool gas(60,000 80,000 oK)May be seen as dark filaments against the bright background of the photosphere空间天气（Space Weath

10、er）Solar AuroraSound waves produced by a solar flare 5 minutesCoronal mass ejections冕洞（Coronal Holes）X-ray images of the sun reveal coronal holes.These arise at the foot points of open field lines and are the origin of the solar wind.能量产生（Energy Production）Energy generation in the sun(and all other

11、stars):Nuclear Fusion=fusing together 2 or more lighter nuclei to produce heavier ones.Nuclear fusion can produce energy up to the production of iron;For elements heavier than iron,energy is gained by nuclear fission.Binding energy due to strong force=on short range,strongest of the 4 known forces:e

12、lectromagnetic,weak,strong,gravitational太阳内部能力产生：质子质子链（The Proton-Proton Chain）Basic reaction:4 1H 4He+energy4 protons have 0.048*10-27 kg(=0.7%)more mass than 4He.Energy gain=Dm*c2=0.43*10-11 Jper reaction.Need large proton speed(high temperature)to overcome Coulomb barrier(electromagnetic repulsio

13、n between protons).Sun needs 1038 reactions,transforming 5 million tons of mass into energy every second,to resist its own gravity.T 107 0K=10 million 0K太阳中微子问题The Solar Neutrino ProblemThe solar interior can not be observed directly because it is highly opaque to radiation.But neutrinos can penetra

14、te huge amounts of material without being absorbed.Davis solar neutrino experimentEarly solar neutrino experiments detected a much lower flux of neutrinos than expected(the“solar neutrino problem”).Recent results have proven that neutrinos change(“oscillate”)between different types(“flavors”),thus s

15、olving the solar neutrino problem.1.1.2 太阳系行星行星大小Assume,we reduce all bodies in the solar system so that the Earth has diameter 0.3 mm.Mercury,Venus,Earth,Mars:size of a grain of salt.Sun:size of a small plum.Jupiter:size of an apple seed.Saturn:slightly smaller than Jupiters“apple seed”.Pluto:Speck

16、 of pepper.八大行星参数行星到 太阳距离（天文单位）公转周期（天）轨道偏心率质量（千克）赤道半径（103千米）平均密度（103千克/米3）表面重力加速度（米/秒2）逃逸速度（米/秒）已知卫星数（个）水星 0.387 87.97 0.206 3.310232.44 5.43 3.63 4.3 0金星 0.723 324.7 0.007 4.8710246.07 5.25 8.60 10.3 0地球 1.000 365.256 0.017 5.97610246.378 5.52 9.82 11.2 1火星 1.524 686.98 0.093 6.4210233.395 3.96 3.7

17、6 5.0 2木星 5.205 4 332.6 0.048 1.989102771.4 1.33 25.92 59.5 18土星 9.576 10 759 0.055 5.684102660.0 0.70 11.29 35.6 23天王星 19.28 30 685 0.051 8.686102525.9 1.24 11.49 21.4 15海王星 30.13 60 189 0.006 1.029102624.75 1.66 11.59 23.6 6冥王星 39.87 90 465 0.256 1.3110221.10 2.34 0.72 1.26 1行星轨道PlutoNeptuneUranus

18、SaturnJupiterMarsEarthVenusMercuryAll planets in almost circular(elliptical)orbits around the sun,in approx.the same plane(ecliptic).Sense of revolution:counter-clockwiseSense of rotation:counter-clockwise(with exception of Venus,Uranus,and Pluto)Orbits generally inclined by no more than 3.4oExcepti

19、ons:Mercury(7o)Pluto(17.2o)(Distances and times reproduced to scale)行星分类（Two Kinds of Planets）Planets of our solar system can be divided into two very different kinds:类地行星Terrestrial(earthlike)planets:Mercury,Venus,Earth,Mars类木行星Jovian(Jupiter-like)planets:Jupiter,Saturn,Uranus,Neptune类地行星（Terrestri

20、al Planets）Four inner planets of Four inner planets of the solar system the solar systemRelatively small in size Relatively small in size and mass(Earth is the and mass(Earth is the largest and most largest and most massive)massive)Rocky surface Rocky surfaceSurface of Venus can not be seen directly from Earth because of its dense cloud cover.行星表面环形山（Craters on Planets Surfaces）Craters(like on our Moons surface)are common throughout the Solar System.Not seen on Jovian planets because they dont have a solid surface.类木行星（The Jovian Planets）平均密度低，都有光环，大都是气体，没有固体表面