  Pasterski, Shao and Strominger have recently proposed that massless
scattering amplitudes can be mapped to correlators on the celestial sphere at
infinity via a Mellin transform. We apply this prescription to arbitrary
$n$-point tree-level gluon amplitudes. The Mellin transforms of MHV amplitudes
are given by generalized hypergeometric functions on the Grassmannian
$Gr(4,n)$, while generic non-MHV amplitudes are given by more complicated
Gelfand $A$-hypergeometric functions.
