Since the density wave theory was introduced by Lin and Shu (1964) to explain the spiral structure considerable effort has been made to detect this kind of wave in our galaxy and to determine its parameters. Observations of the distribution and velocity field of gas and young objects show the present shape and location of the spiral pattern in our galaxy but tell little about its angular velocity. It was proposed by Strömgren (1967) to estimate this important parameter by calculating the places of formation of moderately young stars for which accurate space velocities and ages are known. This was done assuming that the majority of stars is formed in spiral arms so that the stellar birthplaces would outline the position of the spiral pattern at different epochs. Later, Yuan (1969) and Wielen (1973) calculated stellar birthplaces in the spiral potential given by Lin et al. (1969). These investigations showed no disagreement with the assumed density wave, however, the number of stars was too small to verify the assumed pattern speed.