Optical image of an extensive air shower

Photons which constitute a shower image are not emitted simultaneously, but come from a range of shower front positions along the shower path. A spati al distribution of points of origin of photons arriving simultaneously to t he eye is determined in this paper. Using realistic distribution of particl es in a shower, and taking atmospheric scattering of light into account, th e distribution of light arriving simultaneously to a detector is obtained. This instantaneous image ("a snapshot") of the shower is independent of the detector properties - this is "what the shower looks like" when recorded w ith an ideal detector. (C) 2001 Elsevier Science B.V. All rights reserved.