The two known oldest Armenian calendars – Haykian and Protohaykian calendars were closely associated with observations of heavenly bodies. Particularly, in the Haykian calendar since 2341 BC, the main feast of the year was being determined by observing the heliacal rising of the main star of Orion. In the preceding Protohaykian calendar, the same star was used to check both the beginning and the end of the year. Only the period when this star was available for observations was considered as a year. The year in this calendar started with the heliacal rising of Betelgeuse star and ended with its heliacal setting. The rest of the time was considered as out of year.

The analysis of the rock engraving on the upper platform of the Small Hill in Metsamor shows that it represents the image of the well-known Pleiades asterism (stellar cluster M45) as it appears on the horizon while observing its heliacal rising from that place. Meanwhile the central line of the engraving shows the direction of Pleiades’ rising in 9000 BC. At the time, Pleiades shows the direction of the spot of winter solstice. Therefore, the observations of Pleiades from Metsamor could serve as a means to check the exact time of winter solstice.