All stars, including the sun are basically blackbodies. In approximately 5 billi
ID: 1429493 • Letter: A
Question
All stars, including the sun are basically blackbodies. In approximately 5 billion years time, the sun will expand to become a red giant. During this time the Sun’s luminosity will increase to about 1000 times greater than it is now but its surface temperature will decrease to ~3500K. How much more solar energy will fall on the Earth compared to the current value? Hence, in order to maintain thermal equilibrium, each square meter of the Earth’s surface will have to radiate more energy. Currently the Earth radiates approximately as a blackbody and has an average surface temperature of 9ºC. Calculate what the Earth’s surface temperature will be during this red giant phase
Explanation / Answer
rate of energy transer H = dQ/dt = Ae (sigma) T^4
where A = area = 4pir^2, e= emissitivity = (1 for black bdoy)
sigma = constant = 5.67*10^-8
T = temperatrue in kelvin
so Hnew/Hcurrent = (3500^4)/(9+273)^4
Hnew = 2.37*10^4 times larger than current vaues
--------------------------