The dependence of the primary maximum phases derived from Eq. (7) on time. ∇ – BV photometry (Provin 1953), full circle – UV photometry from OAO-2 satellite (Molnar 1975); ◇ – 10-color medium-band photometry (Musielok & Madej 1988); □ – Hipparcos photometry (ESA 1997);  △  ubvy photometry of Pyper & Adelman (1985), the oblique line represents the Guthnick’s ephemeris from Eq. (1), and the star on it the phase position to which are referred the spectroscopic maps we used.