A metric space $(X,d)$ in which for every $x,y\in X$ and
for every $t$, $0 \leq t\leq 1$ there exists exactly one point $z\in
X$ such that $d(x,z)=(1-t)d(x,y)$ and $d(z,y)=td(x,y)$ is called an
M-space. In this paper we discuss suns and moons in M-spaces and
characterize these via best approximation thereby extending
corresponding known results in normed linear spaces to M-spaces.