In this paper, we have solved the Eliashberg equation for T=Tc, obtaining a series expression for the superconducting critical temperature Tc=α0(μ*)(λ〈ω2〉)1/2{1+1/λα1(μ*)〈ω4>/〈ω2>2+1/λ2(α21(μ*)〈ω6>/〈ω2>3+α22(μ*)〈ω4>2/〈ω2>4) +1/λ3(α31(μ*)〈ω8>/〈ω2>4+α32(μ*)(〈ω4>〈ω6>)/〈ω2>5)+α33(μ*)〈ω4>3/〈ω2>6+……}, where α0(μ*), α1(μ*) etc. depend upon μ* only. This new Tc formula shows that Tc is determined not only by λ, 〈ω2〉 and μ*, but also by the various moments 〈ω2n〉 of the effective phonon spectrum.