The temperature of Heaven can be rather accurately computed.  Our
authority is Isaiah 30:26, "Moreover, the light of the Moon shall be as
the light of the Sun and the light of the Sun shall be sevenfold, as
the light of seven days."  Thus Heaven receives from the Moon as much
radiation as we do from the Sun, and in addition 7*7 (49) times as much
as the Earth does from the Sun, or 50 times in all.  The light we
receive from the Moon is one 1/10,000 of the light we receive from the
Sun, so we can ignore that ... The radiation falling on Heaven will
heat it to the point where the heat lost by radiation is just equal to
the heat received by radiation, i.e., Heaven loses 50 times as much
heat as the Earth by radiation.  Using the Stefan-Boltzmann law for
radiation, (_H/_E)^4 = 50, where _E is the absolute temperature of the
earth (-300K), gives _H as 798K (525C).  The exact temperature of Hell
cannot be computed ... [However] Revelations 21:8 says "But the
fearful, and unbelieving ... shall have their part in the lake which
burneth with fire and brimstone."  A lake of molten brimstone means
that its temperature must be at or below the boiling point, 444.6C.  We
have, then, that Heaven, at 525C is hotter than Hell at 445C.
               -- From "Applied Optics" vol. 11, A14, 1972