AST-L4-ch4__3

AST-L4-ch4__3 - Planets Stars and Galaxies Review...

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1 AST 1002 Planets, Stars and Galaxies Section 1 -- MW 3:35-4:50 pm; Section 2 -- MW 5:15-6:30 pm c l ass webs i te – has sy ll abus , s c hedu l e , et c. http: / / www . phy s i c s. f s u . edu / u s er s / Li nd /A S T1002 / defau l t . htm Today’s Lecture: purpose & goals Motions in the Sky 1: Earth, Moon, & Sun” Review Understand that the Moon Revolves Around the Earth -- leads to the phases of the Moon Understand that the Earth and Moon cast shadows from the Sun -- leads to Eclipses Understand that the Earth orbits the Sun in a tilted orbit -- leads to the Seasons Summary Prof. David Lind, FSU Physics te l es c ope w i th l arge aperture te l es c ope w i th sma ll aperture te l es c ope w i th med i um aperture A i Review: Three Powers of a Telescope A telescope is a device to “see far as if near” To “see far as if near” a telescope must have: the ability to detect very faint objects : called Light Light- Gathering Power . Dependent on the diameter of the telescope aperture – the bigger the better! light pollution the ability to separate the images of two objects very close together: called the Angular Resolution . Dependent on the diameter of the telescope aperture – again the bigger the better! seeing the ability to visibly expand the size of images: called Magnification . Dependent only on the curvature of the telescope optics (focal length). LGP 2 /LGP 1 = A 2 /A /A 1 = (D (D 2 /D /D 1 ) 2 α (arcsec) = 2.0x10 -3 x λ (Å) /D (cm) M = f o /f e Atoms and Starlight – Astronomers are forced to be observers we must extract as much information as possible from the starlight. how light interacts with matter . The star’s temperature “blackbody” or Planck radiation is emitted by all warm objects Wien’s law and the Stefan- Boltzmann law (next page) The star’s composition light interacts with the electron energy levels in atoms. quantum model of atoms The relative motion of the star and the observer Doppler effect Review: Light – “the Starry Messenger” λ 1 2 = E 2 – E 1 hc
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2 Temperature and Radiation Examples: Wien’s Law: T (K) = 2,900,000/ λ max (nm) T (K) = 2,900,000 /480 = 6040 I f one star has a sur f a c e temperature o f 6000K , and a se c ond star w i th the same sur f a c e area has a temperature o f 2000K , how mu c h br i ghter w ill the f i rst star be ? Stefan-Boltzmann Law: L = 4 π R 2 . σ T 4 use ratios to solve: I f a star em i ts rad i at i on most strong l y at a wave l ength o f 480 nm , what i s the sur f a c e temperature o f that star ? K L 1 /L 2 = 4 π R 1 2 . σ T 1 4 / 4 π R 2 2 . σ T 2 4 = ( R 1 /R 2 ) 2 . ( T 1 /T 2 ) 4 = 1/1 2 . ( 6000/2000) 4 = ( 3/1) 4 = 81 Reminder – Classroom etiquette Be prepared when you come to class: Read the course material before c om i ng to c l a ss Have with you pencil, paper, calculator ; there may be a quiz!
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