The main plane of a late type galaxy is best determined by its population I components : young stars, gas and dust. In the case of M82 the determination of its principal plane is complicated by its very irregular appearance and the presence of scattered light. We have used three-colour UBV-photometry of this galaxy to determine the stellar population, using the extinction- free parameter Q = (U-B) − 0.65(B-V), and the extinction AB = 4 ((B-V) − (B-V)oo; (B-V)oo being the intrinsic colour of the

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... population, taken, e.g. from population synthesis calculations. Corrections for scattered light were made using the degree of polarization as well as the excess ultraviolet light (see Notni and Bronkalla, 1983; Notni et al., 1981 for details).