  We develop a split representation for celestial amplitudes in celestial
holography, by cutting internal lines of Feynman diagrams in Minkowski space.
More explicitly, the bulk-to-bulk propagators associated with the internal
lines are expressed as a product of two boundary-to-bulk propagators with a
coinciding boundary point integrated over the celestial sphere. Applying this
split representation, we compute the conformal partial wave and conformal block
expansions of celestial four-point functions of massless scalars and photons on
the Euclidean celestial sphere. In the $t$-channel massless scalar amplitude,
we observe novel intermediate exchanges of staggered modules in the conformal
block expansion.
