Question
SLPaper 2
1.[1]
Show that the apparent brightness b ∝ AT⁴/d², where d is the distance of the object from Earth, T is the surface temperature of the object and A is the surface area of the object.
Verified
Solution
substitution of L=σAT^4 into b=L/(4πd^2) giving b=(σAT^4)/(4πd^2)
2.[2]
Two of the brightest objects in the night sky seen from Earth are the planet Venus and the star Sirius. Explain why the equation b ∝ AT⁴/d² is applicable to Sirius but not to Venus.
Verified
Solution
equation applies to Sirius/stars that are luminous/emit light «from fusion»
but Venus reflects the Sun's light/does not emit light «from fusion»
