Midterm Solutions

# 2 au from the sun in wm2 flux luminosityarea l4d2

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Unformatted text preview: is 4.74, and using the standard definition of magnitude: Mbol(Vega) – Mbol(Sun) =  ­2.5log10(LVega/LSun) =&gt; LVega = LSun x 10 ­0.4(0.72 ­4.74) = 41 LSun L = 4πR2σT4 =&gt; R = (L/4πσT4)1/2 Or in solar units: (R/R¤) = (L/L¤)1/2(T/T¤) ­2 = (41)1/2(9600/5800) ­2 R = 2.3 R¤ This is a dwarf star. (f) [10 pts] What is the apparent angular size (diameter) of Vega in arcseconds as viewed from Earth? Can this be resolved with the Keck telescopes (resolution ≈ 0.05 arcseconds) θ (“) = diameter (AU) / distance (pc) = 2 x radius (AU) / distance (pc) = 2 x (2.3 R¤) x (6.96x108 m/R¤) x (AU/1.50x1011 m) / 7.7 pc = 2.8x10 ­3 arcseconds or 2.8 milliarcseconds This could not be resolved with Keck. Page 6 of 16 Physics 160 Fall 2013 Midterm Exam (2) [Total: 50 pt] Taking Jupiter’s Temperature. (a) [5 pts] What is the radiant flux received at Jupiter (orbital rad...
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