Due to their proximity to the latter, Kochab (top right) and Perkhad (bottom left) are known as the Polo Guardians.
Kochab is an orange giant 130 times brighter than the Sun. The star has reached an evolutionary stage where it has run out of nuclear fuel and has expanded to a diameter of 42 solar diameters. Its mass has not yet been obtained directly: from its position on the HR diagram a value of 2.2 solar masses has been estimated, while from its surface gravity a value of 2.5 solar masses has been obtained.
Kochab played a crucial role in ancient culture, particularly in Egypt.
Because of the precession phenomenon of the equinoxes, the star indicating the pole varies through time. In our days the north celestial pole is indicated by the North Star, while before the year 2500 B.C. to identify the north was used Thuban, in the constellation of the Dragon.
In the interlude, approximately between 2500 B.C. and the early centuries after the year zero, no particularly brilliant stars were located near the celestial north pole.
To identify the north, the populations of that time, especially the Ancient Egyptians, exploited alignments between Kochab and Mizar, a star of the Ursa Major. According to some researchers, it is because of these alignments that the Egyptians were able to orient their pyramids almost perfectly to the north.
Credit: Wikiski.
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