 He found that cairns E and O were aligned in the direction of summer solstice sunrise, using cairn E for a backsight and cairn O as a foresight, and that cairns C and O were aligned in the direction of summer solstice sunset, using C as a backsight and O as a foresight.Further, he found that cairn pairs FO, FA, and FB correspond to the rising points of the stars Sirius, Aldebaran, and Rigel, respectively.Observing the first yearly heliacal rising of these stars would have been an effective tool for determining the progress of the solar year, as the first heliacal rise of a star occurs on the same date (relative to the solstices) each year.