  We use a high-precision Monte Carlo simulation to determine the universal
specific-heat amplitude ratio A+/A- in the three-dimensional Ising model via
the impact angle \phi of complex temperature zeros. We also measure the
correlation-length critical exponent \nu from finite-size scaling, and the
specific-heat exponent \alpha through hyperscaling. Extrapolations to the
thermodynamic limit yield \phi = 59.2(1.0) degrees, A+/A- = 0.56(3), \nu =
0.63048(32) and \alpha = 0.1086(10). These results are compatible with some
previous estimates from a variety of sources and rule out recently conjectured
exact values.
