Abstract New approaches to the history of the Old Rus’ chronicles have been developed and widely discussed in recent decades. But chronological systems which used by first chroniclers very poorly studied. The use of solar activity data makes it possible to draw on information about indirect manifestations of solar activity to establish the eras in which chronographic (annual) dates were given in the Tale of Bygone Years. In particular, this makes it possible to identify a number of messages from the Tale of Bygone Years, the annual dates of which are given for the Annian era, which consisted of 5500 years from the Creation of the World before AD. This is the basis for the hypothesis that one of the sources used by the compiler of the Tale of Bygone Years gave annual dates by the Annian era.
Keywords: solar activity, historical chronology, textual criticism, Old Rus' chronicles