Diffuse light near zeta Orionis and the Horsehead Nebula, and anomalous extinction of HD 37903, as measured with the ANS.

The light of Ori, reflected by the diffuse interstellar medium to the SSE of this star, was measured with the uVinstrument on board of the ANS. The diffuse light is bluer than the light of the stars. Possible contributions of emission by the gas are discussed. The gradient of the surface brightness in this region in front of the dark cloud L 1630 is steeper than the gradients reported from the OAO-2 and TD1 satellites, indicating a complicated geometry for the scattering material. The normalised surface brightness is small and can be understood as due to unfavourable scattering geometry or due to a small optical depth of the scattering material.

The extinction of HD 37903 in L 1630 is found to be anomalous: it is almost normal shortward of 2500 Å, but excessive by up to 0.4 mag between 5000 and 2700 Å.