The kurgans of the Sintashta culture. The Sintashta culture phasicly corresponds to the Middle Bronze Age of the region and dates (within traditional «brief» chronology) to the 18-16 centuries BC. The calibrated radiocarbon dates mostly fall between the 21 and 18 centuries BC.
Kurgan 25 of the Bolshekaragansky cemetery (the necropolis of the fortified settlement Arkaim) became the main object for archaeoastonomic research. During the process of excavation the mound of the kurgan was cleared to reveal a round ground with a diameter of 18-18,5m, surrounded by a ditch. Human burials and animal sacrifices had been performed on the ground and in the ditch over several decades. There is a total of 14 grave pits and 6 sacrificial pits. The sacrificial pits are localized in the southern part of the kurgan. The complex of grave pits had three or four stages of formation. First was the eastern group of burials, then the central one. On the last stage of functioning of the complex the additional burials appear in the ditch and near the ditch from the west.
Astronomic observation were significant for choosing the place to build a kurgan. The location of the kurgan corresponds to the azimuth of rising of the lower edge of the sun (48,3°), set from the geometric center of the settlement Arkaim on the day of summer solstice for the age of2000 years BC if obse rving the event from ground surface.
The observations of heavenly bodies rising and setting were significant for the organization of the inner space of the necropolis. The observations were performed from the center of underkurgan ground or through the central point if the observer was outside the ground. Seemingly, the azimuths of rising and setting of the «high» moon on the day of summer solstice were of primary significance during the marking-out of the complex. These azimuths determine the borders of the sector of early burials (36°-144°) and the location of the entrance to the underkurgan ground. The system of sights (post structures in the ditch) is related to the observation of these astronomic events.
The azimuths of rising and setting of the moon at the utmost positions also determine the borders of the sector meant for construction of sacrificial pits. The western border of this sector corresponds with the azimuth of full «low» moon setting on the day of summer solstice (236°), and the eastern one coincides with the azimuth of full «high» moon rising on the same day (144°).
The central grave pits 9 and 10 are special within the system of the kurgan. Laying near the geometric center of the ground and being oriented according to the cardinal points, they make up a common system with the circumference of the circular ditch. The northern point in their orientation is deviated 7-10 to the east. It can be related to the nightly observation of the North Star which belonged to the Dragon constellation at that time.
The position of the most northern grave of the group of burials in the filling of the ditch from the west corresponds with the azimuth of sunset on the day of summer solstice (317°) if it is observed from the center of the kurgan.
Specifically interesting from the point of view of archaeoastronomy is the ditch of the kurgan. It is not continuous, but consists of 12 sections. The presence of 30 sections in the design of the ditch allowed to suppose materialization of a model of solar zodiac.
To test this supposition, the plan of the kurgan was superposed with the image of ecliptic with directions on the borders of modern zodiac constellations and the brightest stars of northern hemisphere close to the plane of the ecliptic. A celestial map of 1950 was used. The best correspondence between the images was obtained by relative rotation with matching the axes of the images. The correspondences with the following stars were found: a of Canis Minor — Procyon, a of Leo — Regulus, P of Leo — Denebola, a of Virgo — Spika, a of Bootes — Arcturus, a of Scorpio — Antares, the central part of the Archer, a of Eagle—Altair. All of these were rising stars on the latitude of Arkaim (a=+52,6°) at the time of the existence of the settlement. The positions of two more bright stars of northern hemisphere — Sirius (a of Canis Major) and Aldebaran (a of Taurus) were probably marked by posts in the eastern semicircle of the ditch.
It is possible to suppose that the point of spring equinox coincides with the direction to the east and the point of autumn equinox coincides with the direction to the west. Such model corresponds to actual movement of the sun on the ecliptic during the year. Then the point of spring equinox coincides in our model with the position of Pleiades. Knowing the period of precession we can calculate the zodiac age reflected in the design of the kurgan. It corresponds to the year 2080 BC. As we can see, the dates obtained using archaeoastronomic methods do not contradict with the calibrated radiocarbon ones.