- Mari Garcia
The Pole Star: a Never-Ending Story
Over the history of human civilizations, the Pole Star, visible from northern hemisphere, has been used as a beacon to mariners, navigators and travellers as well as astronomers to help determine the latitude of any place. However, as a consequence of the phenomena known as the precession of the equinoxes, the role of the North Star as a guiding light has passed from one star to another over time.
A Pole Star is a visible star, usually a prominent one that aligns closely with the Earth’s axis of rotation. This means that the star’s apparent position is close to the celestial pole and is directly overhead when viewed from either of the Earth’s North or South Pole. Potentially there are both northern and southern pole stars but this depends on the current sidereal positions. The term pole star is also known as “north star” in the northern hemisphere.
Pole stars change over time as a result of the Earth’s rotation axis. If the stars were fixed in space, precession would cause the celestial pole to trace imaginary circle every 25 770 years, passing close to stars at different times. But stars also move relative to each other and so this is also called ‘proper motion’ and is another factor which causes the apparent drift of the pole star.
Pole Stars have been used in navigation because other stars’ positions change during the course of the night but the pole star’s positions does not. This makes the pole star a reliable indicator of direction toward the respective pole. Also, their angle of elevation i.e. the angular distance above the horizon, is used to determine latitude.
If we go back to 3000 bce, the star Thuban, the alpha star of the constellation Draco fulfilled this role. Draco is a faint star and is not as bright as the current North Star, Polaris. In today’s urban skies, it is almost invisible due to pollution and the proliferation of other artificial light sources.
A few thousand years later, during the first millennium bce, a bright star Ursae Minoris was the closest to the celestial pole however it was never considered to be close enough to qualify for the role as the marker of the celestial pole. As a consequence, commentators of the era such as the Greek navigator Pytheas (ca 320 bce) described the celestial pole as “devoid of stars”.
During the era of the Roman Empire, Ursae Minoris was described as “always visible” by Stobbaeus in the fifth century and was also known as the scip-steorra, the “ship-star” in 10th century Anglo-Saxon England. This reflects its importance in navigation.
From about the 16th century, the term stella polaris was used to refer to Ursae Minoris although at the time the star itself was still several degrees away from the celestial pole.
The importance of the pole star cannot be overstated as it serves as the hour hand in the celestial clock of precession. The cycle of precession takes about 25 770 years to complete a cycle. This means that the current pole star, Polaris will reach maximum declination from the celestial North Pole in 2100.
As each pole star becomes prominent not only in the heavens as the celestial pole aligns itself to it, the mythology of the star and/or constellation is mirrored in human civilizations. Thuban, the alpha star of the constellation, Draco was the pole star from 3942 BC, until 1793 BCE during the time of the ancient Egyptians. This ‘dragon’ was enshrined in world cosmologies as diverse as the Egyptians, the Greeks, the Romans and the peoples of the Americas, Asia and indigenous Australia. The importance of the pole star is seen again and again over many centuries enshrined in buildings like the pyramids, celebrated in ritual and elaborated on in myth.
As stars close to the pole never set, the ancient Egyptians described these stars as “imperishable” or “undying”. When the Pharaoh Khufu built the Great Pyramid around 2550 BCE, he expected that when he died, he would join not only with the Sun, but with Thuban as well, maintaining order in the celestial realm, just as he had on Earth. He was buried in the largest of the Giza pyramids when he died and his burial chamber was fashioned deep inside the Great Pyramid and two skinny shafts bore outward from the chamber aligned to Thuban, thereby providing a celestial path for the Pharaoh’s soul to be reunited with the pole star.
Polaris, the current pole star, has been known by many names including ‘the Pathway’, ‘the Pointer’ - indicating the way; ‘Navel of the World’, ‘Gate of Heaven’, ‘Hub of the Cosmos’, ‘the Highest Peak of the World Mountain’, ‘Lodestar’, ‘the Steering Star’, ‘the Ship Star’ and Stella Maris , ‘Star of the Sea". It is no coincidence that its rise to prominence as the pole star has marked a period in human history which reflects the movement of populations both geographically and philosophically. Polaris, has been honoured since Phoenician times, and has lured countless souls into adventure and exploration for it was known as a fixed and true beacon that would guide any lost soul home or on to their true destiny. The motion of the stars around the pivot star Polaris has long been thought of as being a great celestial mill, with the stars like grains of wheat spinning on the large circular milling stone. We can postulate that philosophical and religious concepts which revolve around the notion of ‘the path’, ‘the way’ and references to ‘the journey’ all reflect the collective reflection of Polaris in the collective psyche.
Looking into the future, Errai will become the northern pole star around 4000 AD and Alderamin will take its turn around 7500 AD.