  A 1+3 dimensional solution of relativistic hydrodynamics is analyzed in this
paper. Momentum distribution and other observables are calculated from the
solution and compared to hadronic measurements from the Relativistic Heavy Ion
Collider (RHIC). The solution is compatible with the data, but only the
freeze-out point of the evolution is determined. Many equation of states and
initial states (initial temperatures) are valid with the same freeze-out
distribution, thus the same hadronic observables. The observable that would
distinguish between these initial temperatures is momentum distribution of
photons, as photons are created throughout the evolution of the fireball
created in RHIC collisions. The PHENIX experiment at RHIC measures such data
via low invariant mass e+e- pairs. Average temperature from this data is
T=221+-23+-18 MeV, while a model calculation with initial temperature 370 MeV
agree with the data.
