  A new analytical criterion that captures the onset of separation of flow past
elliptic cylinders is derived by considering the variation of the wall normal
velocity in Reynolds number parameter space. It is shown that this criterion
can be used to calculate the separation Reynolds number Re_s for the classical
problem of flow past a circular cylinder, a contentious and unresolved issue
till date. The two dimensional Navier-Stokes equations are solved
computationally and an exact value of Re_s is obtained by applying the
aforementioned criterion.
