As we know the old Armenian Haykian calendar was a typical solar one and has 12 x 30 days + 5 days = 365 days structure. The year in this calendar consists of 12 months 30 days each and thus contains only 360 days. After these 360 days of year 5 additional days were added to complete the year cycle. The beginning of this calendar was calculated to be in 2341 BC. The main holiday of this calendar - Nawasard has been fixed and the day of this feast was determined by observing the heliacal rising of the star α Orionis – Betelgeuse which takes place 8 days before summer solstice. The calendar that was in use in Armenia before the Haykian one was completely based on star observations. The year in this calendar has 10 x 30 days + 70(65) days = 365.2422 days structure. Only the period of time when the main star of the heavenly image of the Supreme Being was visible in the sky was considered as year, while the time when this star was not visible was considered to be out of year and this was a period of different taboo. The year in this calendar consists of 10 months 30 days each and thus contains only 300 days. After these 300 days of year a 70(65) days out of year period was added. Although the existence and the structure of Protohaykian calendar are proved by mediaeval Armenian historical sources, Armenian folklore sources, folklore of neighboring nations, calendars of some neighboring nations, and the analyze of ornaments on a ceramic vessel of XXXII c. BC from Keti (Shirak, Armenia) the beginning of this calendar is unknown yet.

Here an attempt is made to calculate and find out the date of the beginning of Protohaykian calendar. First it was shown that in the case when we have too long use of determination of fixed days by means of observations of heliacal risings of stars in any calendar there must be changed either the day fixed by the observations or else the star used for that determination. In the case of Protohaykian calendar the day of the main holiday could not be changed as it was correlated with the day of the harvest of winter crops. So the star used to check the day of the main feast must be changed. It is shown that at the period of the establishment of Protohaykian calendar the heliacal rising of the star Spica – α Virgo was used to determine the day of the main holiday. Our calculations show that the heliacal rising of α Virgo was observable from Armenia 8 days before summer solstice in 9000 BC. Thus, we assume that the Protohaykian calendar was established in 9000 BC. This date is in good correlation with the time of observation of Pleiades from the observational platform of the Small Hill in Metsamor. We have also good correlation with geological data concerning the time of drying of so-called Araratian see existing in the region of modern Araratian valley from 780000 until 12000 BC and the time of cultivation of crops in Armenia about 12000 years ago.