(光度光的强度)课件

Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,The Sky,Chapter 2,0,The previous chapter took you on a cosmic zoom to explore the universe in space and time.That quick preview only sets the stage for the drama to come.Now it is time to return to Earth and look closely at the sky.To understand what you are in the universe,you must know where you are.As you look at the sky,you can answer three essential questions:,How do astronomers refer to stars by name and brightness?,How does the sky move as Earth moves?,How does the sky affect Earth?,Guidepost,0,Answering those questions will tell you a great deal about yourself and your home on planet Earth.Three additional questions will tell you more about how science works.,How do we know?,What is a scientific model?,How do we know?,What is the difference between a science and a pseudoscience?,How do we know?,Why is evidence critical in science?,In the next chapter,you will study the motions of the moon and discover yet another way that motions in the sky affect your life on Earth.,Guidepost(continued),0,I.The Stars,A.Constellations,(,星座,),B.The Names of the Stars,C.The Brightness(,亮度,),of Stars,D.Magnitude(,星等,),and Intensity,(,光度,=,光的強度,),II.The Sky and Its Motion,A.The Celestial Sphere,天球,B.Precession,進動,III.The Cycles of the Sun,A.The Annual Motion of the Sun,B.The Seasons,C.The Moving Planets,Outline,0,V.Astronomical Influences on Earths Climate,A.The Hypothesis,B.The Evidence,Outline(continued),0,Constellations,In ancient times,constellations only referred to the brightest stars that appeared to form groups.,0,Constellations(2),They were believed to represent great heroes and mythological figures.Their position in the sky seemed to tell stories that were handed down from generation to generation over thousands of years.,0,Constellations(3),Today,constellations are well-defined regions on the sky,irrespective of the presence or absence of bright stars in those regions.,0,Constellations(4),The stars of a constellation only appear to be close to one another.,Usually,this is only a,projection effect,.,The stars of a constellation may be located at very different distances from us.,0,Constellations(5),Stars are named by a Greek letter(,a,b,g,)according to their relative brightness within a given constellation+the possessive form of the name of the constellation:,Orion,Betelgeuse,Rigel,Rigel=,b,Orionis,0,Betelgeuse=,a,Orionis,Constellations(6),0,Some examples of easily recognizable constellations and their brightest stars,The Magnitude Scale,First introduced by Hipparchus(160-127 B.C.):,Brightest stars:1,st,magnitude,Faintest stars(unaided eye):6,th,magnitude,0,More quantitative:,1,st,mag.stars appear 100 times brighter than 6,th,mag.stars,1 mag.difference gives a factor of 2.512 in apparent brightness(larger magnitude=fainter object!),Betelgeuse,Rigel,Magnitude=0.41 mag,Magnitude=0.14 mag,The Magnitude Scale(Example),Magn.Diff.,Intensity Ratio,1,2.512,2,2.512*2.512=(2.512),2,=6.31,5,(2.512),5,=100,For a magnitude difference of 0.41 0.14=0.27,we find an intensity ratio of(2.512),0.27,=1.28.,0,In other words:Rigel is 1.28 times brighter than Betelgeuse.,The Magnitude Scale(2),Sirius(brightest star in the night sky):m,v,=-1.42Full moon:m,v,=-12.5Sun:m,v,=-26.5,The magnitude scale system can be extended towards negative numbers(very bright)and numbers greater than 6(faint objects):,0,The Celestial Sphere,Celestial equator=projection of Earths equator onto the c.s.,Zenith=Point on the celestial sphere directly overhead,0,Nadir=Point on the c.s.directly underneath(not visible!),North celestial pole=projection of Earths north pole onto the c.s.,Distances on the Celestial Sphere,The,distance between two stars on the celestial sphere,can only be given as the difference between the,directions,in which we see the stars.,0,Therefore,distances on the celestial sphere are measured as angles,i.e.,in,degrees(,o,):,Full circle=360,o,arc minutes():,1,o,=60,arc seconds(“):,1,=60”,The Celestial Sphere(2),From geographic latitude,l,(northern hemisphere),you see the celestial north pole,l,degrees above the northern horizon;,l,90,o,-,l,Celestial equator culminates 90,l,above the horizon.,From geographic latitude,l,(southern hemisphere),you see the celestial south pole,l,degrees above the southern horizon.,0,The Celestial Sphere(Example),The Celestial South Pole is,not,visible from the northern hemisphere.,Horizon,North,Celestial North Pole,40.7,0,South,49.3,0,Celestial Equator,Horizon,New York City:,l,40.7,0,The Celestial Sphere(3),0,Apparent Motion of The Celestial Sphere,0,Looking north,you will see stars apparently circling counterclockwise around the Celestial North Pole.,Apparent Motion of The Celestial Sphere(2),0,Some constellations around the Celestial North Pole never set.These are called,“circumpolar”.,The circle on the celestial sphere containing the circumpolar constellations is called the,“circumpolar circl