1ASTR 1040 ASTR 1040 AccelAccelAstroAstro::Stars & GalaxiesStars & GalaxiesProf. Prof. JuriJuriToomreToomreTA: Nicholas NelsonTA: Nicholas NelsonLecture 10 Lecture 10 ThurThur10 Feb 1110 Feb 11zeus.colorado.edu/astr1040zeus.colorado.edu/astr1040--toomretoomrePlanetaryPlanetaryNebulaNebulaNGC 3132NGC 3132TodayToday••What can we What can we measuremeasurein other stars?in other stars?••How do we begin to How do we begin to classify other starsclassify other stars? ? ••Why O, B, A Why O, B, A ……such a nutty scheme!such a nutty scheme!••Why Why temperature and spectral linestemperature and spectral linesare are closely closely linkedlinkedin classifying stars in classifying stars O B AO B A……MM••Stars on Stars on ““HertzsprungHertzsprung––RussellRussell””(or H(or H--R) diagram R) diagram comes nextcomes next••ReRe--readreadChap 15, Chap 15, `Surveying the Stars`Surveying the Stars’’••Review tonightReview tonightfor Midfor Mid--Term Exam 1 on MonTerm Exam 1 on Mon••SignSign--up for up for Observatory Night #3Observatory Night #3on Monon MonSummary Clicker Summary Clicker ----Solar WindSolar Wind••What are visible effects of the Earth being What are visible effects of the Earth being ““bathedbathed””in the wind of solar particles, in the wind of solar particles, especially when wind has especially when wind has strong hiccupstrong hiccup??••A.A.“AuroralAurorallightslights””visible at nightvisible at night••B.B.Electric power grids have problemsElectric power grids have problems••C. C. ShortShort--wave radio talk interruptedwave radio talk interrupted••D.D.Satellites (and beepers) may get friedSatellites (and beepers) may get fried••E.E.All of the aboveAll of the aboveE.E.DiscussionDiscussionWhat are effects of solar activity on our What are effects of solar activity on our technological society?technological society?Solar Wind and Solar Wind and AuroraeAuroraeNorthern LightsNorthern Lights(Aurora Borealis)(Aurora Borealis)2Now onward to measuring other stars: Now onward to measuring other stars: Chap 15 Chap 15 ––SURVEYING THE STARSSURVEYING THE STARS••Measuring stellar Measuring stellar luminositiesluminosities••Measuring Measuring distancesdistances••Measuring Measuring temperaturestemperaturesOften only seeing a point of lightOften only seeing a point of light••Stars are Stars are so small so small compared to their distancecompared to their distancethat we almost never have that we almost never have the resolution to see their the resolution to see their sizes and details directly sizes and details directly ––““point sourcespoint sources””••We deduce everything by We deduce everything by measuring the amount of measuring the amount of light light (brightness)(brightness)at at different wavelengths different wavelengths (color, spectra)(color, spectra)So what canSo what canwe find out about we find out about other stars?other stars?APPARENTAPPARENTBRIGHTNESSBRIGHTNESSPOSITION POSITION SPECTRUM SPECTRUM Most Basic Problem in AstronomyMost Basic Problem in AstronomyStar of given Star of given APPARENT BRIGHTNESSAPPARENT BRIGHTNESScould be eithercould be eitherA. very luminous star far away A. very luminous star far away B. low luminosity star closer by B. low luminosity star closer by Need to know the Need to know the DISTANCEDISTANCEto the starto the starInverse Square Law of BrightnessInverse Square Law of BrightnessApparentApparentBrightness Brightness LLoo/ (/ (distancedistance))224 / Luminosity BrightnessApparent Clicker Clicker ––Dimming with distance ?Dimming with distance ?••If you quadruple (x4) your distance to a If you quadruple (x4) your distance to a light and look again, how much dimmer light and look again, how much dimmer does it appear?does it appear?••A.A.oneone--half as bright as originallyhalf as bright as originally••B.B.oneone--fourth as brightfourth as bright••C. C. oneone--eight as brighteight as bright••D.D.oneone--sixteenth as brightsixteenth as bright••E.E.unchanged, since really same lightunchanged, since really same lightD.D.3Stellar LuminosityStellar Luminosity••What we What we measuremeasure: : APPARENT BRIGHTNESSAPPARENT BRIGHTNESSor how bright it appears to us or how bright it appears to us here on Earthhere on Earth••What we What we want to knowwant to know: : (absolute) (absolute) LUMINOSITYLUMINOSITYor how much energy is or how much energy is emitted (joules/sec or watts)emitted (joules/sec or watts)••Need to know Need to know DISTANCEDISTANCEto to the starthe starParallax Parallax ––to determine distanceto determine distanceooMeasure the Measure the apparent apparent movement of starsmovement of starsover a over a yearyearooMovement is caused by Movement is caused by EarthEarth’’s movement around s movement around the Sunthe SunooCloser objects will move Closer objects will move more than farther objectsmore than farther objectsHow Stellar Parallax WorksHow Stellar Parallax WorksClass selfClass self--demo of parallaxdemo of parallax••Your Your nose nose is the Sunis the Sun••Your Your left eyeleft eyeis the Earth in Januaryis the Earth in January••Your Your right eyeright eyeis the Earth in Juneis the Earth in JuneWatch the Watch the apparent motion of your thumbapparent motion of your thumbagainst against a distant reference point (repeat at arma distant reference point (repeat at arm’’s length)s length)Which Which ““movemove””moremore----closer or farther objects?closer or farther objects?Best parallax measurer: Best parallax measurer: HipparcosHipparcossatellitesatellite19891989--19931993••Space measurements not Space measurements not affected by atmosphere affected by atmosphere ••Measurement made Measurement made many times until many times until accurate accurate to 0.001 to 0.001 arcsecarcsec((3300 3300 light years)light years)••100,000 stars mapped100,000 stars mapped••(2.5 million to slightly (2.5 million to slightly lesser accuracy)lesser accuracy)Stellar Parallax:Stellar Parallax:measuring nearbymeasuring nearbydistancesdistances4Measuring SurfaceMeasuring SurfaceTEMPERATURETEMPERATUREShape ofShape ofspectrum goodspectrum good……butbutspectral linesspectral linesmuch bettermuch betterSpectra help classify starsSpectra help classify starsOBAFGKM ?!?OBAFGKM ?!?••Spectral