  We suggest that the Orion A cloud is gravitationally collapsing on large
scales, and is producing the Orion Nebula Cluster due to the focusing effects
of gravity acting within a finite cloud geometry. In support of this
suggestion, we show how an elliptical rotating sheet of gas with a modest
density gradient along the major axis can collapse to produce a structure
qualitatively resembling Orion A, with a fan-shaped structure at one end,
ridges or filaments along the fan, and a narrow curved filament at the other
end reminiscent of the famous integral-shaped filament. The model produces a
local concentration of mass within the narrow filament which in principle could
form a dense cluster of stars like that of the Orion Nebula. We suggest that
global gravitational contraction might be a more common feature of molecular
clouds than previously recognized, and that the formation of star clusters is a
dynamic process resulting from the focusing effects of gravity acting upon the
geometry of finite clouds.
