  Almost a century ago, Einstein used a weak field approximation around
Minkowski space-time to calculate the energy carried away by gravitational
waves emitted by a time changing mass-quadrupole. However, by now there is
strong observational evidence for a positive cosmological constant, $\Lambda$.
To incorporate this fact, Einstein's celebrated derivation is generalized by
replacing Minkowski space-time with de Sitter space-time. The investigation is
motivated by the fact that, because of the significant differences between the
asymptotic structures of Minkowski and de Sitter space-times, many of the
standard techniques, including the standard $1/r$ expansions, can not be used
for $\Lambda >0$. Furthermore since, e.g., the energy carried by gravitational
waves is always positive in Minkowski space-time but can be arbitrarily
negative in de Sitter space-time \emph{irrespective of how small $\Lambda$ is},
the limit $\Lambda\to 0$ can fail to be continuous. Therefore, a priori it is
not clear that a small $\Lambda$ would introduce only negligible corrections to
Einstein's formula. We show that, while even a tiny cosmological constant does
introduce qualitatively new features, in the end, corrections to Einstein's
formula are negligible for astrophysical sources currently under consideration
by gravitational wave observatories.
