Radiation laws – apply to astronomical sources
•Wien’s law :
•         lpeak = 0.289 / T(K) cm 
• lpeak ® color: hotter ® bluer (shorter l)
•                       cooler ® redder (longer l)
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•Greater total energy (summed over all wavelengths) radiated by hotter objects             
•                              Ż
•Stefan’s Law :
•energy radiated/unit area of B-B surface/unit time µ (temp)4
•                       F = sT4
•  Flux  = 5.67x 10-8T4 watt/m2/K4
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•Stefan’s constant = s
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•
For T = 6000 K, lpeak=4800Ĺ
radiation appears yellow
For T = 3000 K, lpeak=9700Ĺ
®near infrared
If T x2, Fx24® 16xpower