The book describes the main stages in the lives, scientific and social activities of famous astronomers and directors of Nikolaev Astronomical Observatory in the first half of XX century, Boris Pavlovich Ostaschenko-Kudryavtzev and Leonid Ivanovich Semenov, who led the Observatory when it became the Nikolaev department of Main Astronomical Observatory at Pulkovo. The book is intended for scientific workers and all those that interested in the history of astronomy at the time of its formation in one of the oldest observatories in Ukraine in Nikolaev city.