>	restart:#"m13_p23"

Find the average emissivity for the Moon, from the energy balance, the mean surface temperature, Tm=274 K, and the bolometric albedo, =0.12.

Datos:

>	read`../therm_const.m`:read`../therm_proc.m`:read`../therm_eq.m`:with(therm_proc):with(RealDomain):

>	dat:=[Tm=274*K_,rho=0.12,E=1370*W_/m_^2];

>	dat:=op(dat),Const,SI2,SI1:

a) Find the average emissivity for the Moon, from the energy balance, the mean surface temperature, Tm=274 K, and the bolometric albedo, =0.12.

>	eqEB:=alpha*Pi*R^2*E=epsilon*4*Pi*R^2*sigma*Tm^4;eqEB_detail:=alpha+rho+tau=1;alpha:=1-rho;epsilon_:=evalf(subs(dat,solve(eqEB,epsilon)));

i.e. la emisividad media de la luna es del 94% (casi como cuerpo negro). La temperatura de cuerpo negro sería:

>	eqEBbb:=Pi*R^2*E=4*Pi*R^2*sigma*Tm_bb^4;Tm_bb_:=solve(%,Tm_bb)[1];Tm_bb__:=simplify(evalf(subs(dat,SI0,Tm_bb_)))*K_;'Tm_bb__'=TKC(%);

i.e. si fuera un cuerpo negro, la luna (y la tierra) estaría a 279 K (6 ºC).

>