The biggest astronomical observatory in Samarkand was built in the 1420s by Ulugbek. Here, during three decades, scholars, including outstanding astronomers Qazi-Zadeh Rumi, Djemshid Giyas ad-Din Kashi and Ali Kushchi studied the skies. Samarkand observatory became famous owing to Ulugbek's book 'Zidj', containing theoretical introduction and a catalogue of 1018 stars. The observatory was discovered by Samarkand archeologist Vyat-kin V.L. at the beginning of the 20th century. He excavated underground remains of a huge quadrant - 40 meter in radius which was used for observation of the Sun, Moon and other bodies.