During the Apollo 8 lunar flight, 3300 kg of liquid oxygen were released from the launch vehicle 45,000 km from the earth during a normal mission operation. The oxygen froze immediately, forming a 500‐km cloud of small particles. The cloud was photographed by the Smithsonian Astrophysical Observatory's satellite tracking station in Spain over a 90‐min period. We have reduced this photometric data, using a simple collisionless model for the expansion, and have deduced the following parameters. The particles that are responsible for the scattering have a bulk velocity of 1.4×104cm/sec and a random velocity of 0.3×104cm/sec. Though we have not yet been able to obtain the size of the scatterers directly, we did establish an estimate of 100–1000 μ for the initial radius of the particles. The particles are subliming, and the radius is given byr0e−t/τs, where τsis approxima