During 2020-2022, as a result of the detailed surveying and ar­chaeo­astronomical study of the monument known as "Zorats Qarer" located near to the Sisian city, Armenia, so-called "observational instruments" composed of stones No 12, 13 and 14 were discovered. The article presents the simul­taneous examination of the same stones for 9000 and 5800 BC. The stars, that could be observed with the help of the stones, their mythological content and the relations between ancient Armenian calendar and conditions of obser­va­tions are disscused. The results obtained by astronomical examination of the stones definitely refer to 9000 BC, at the beginning of the Protoaykian calendar. In other hand, it became clear that as a result of the changes of ce­lestial bodies, it was necessary to make some harmonious changes in mytho­logical concepts, which allowed the use of the same observational stone tools to continue in 5800 BC (possibly even later). The positions of celestial bodies observations and the time regulations in year cycle are in good agreement with the structure of Protohaykian calendar and of the ornament-calendar on vessel from Keti, refered to 4th millennium BC. The changes made in 5800 BC seem to have certain manifestations of the Mithraic cult.