Cosmological Constant in de-Sitter Spacetime

With the basic cosmological relations that agree with the recent observations, simple expressions are suggested concerning the value of cosmological constant($\Lambda$). A large contribution of quantum vacuum to the energy momentum tensor does not agree with the observed cosmos. However,one requires the presence of positive $\Lambda$ to make the various observations consistent. After a review of the effect of cosmological constant on the geodetic motions in the Schwarzschild de Sitter spacetime, some approaches to its solutions are briefly discussed. Also suggested is the very weak limit on $\Lambda$ from the planetary perturbations.