Pole Stars: Friends of Ancient Mariners
Syed Mohd. SalehUddin
(Writer is an Assistant Professor (retd) Rampura Ekramunnessa Degree College and Instructor (retd) of Bangladesh Army Education Corps (SWO) where he used to teach Map reading, Astro Navigation, Aircraft recognition etc subjects in various Bangladesh Army Training establishments.)
To ancient Mariners Pole stars were their great friends. Today also its importance is not less to those mariners whose latest navigational devices become unserviceable in the sea due to some reasons. For navigational purposes ancient mariners could use sun also. Today also it is helping all the mariners by the day. But when night came and mariners were in the deep sea in the past when latest navigational devices were not developed Pole stars were ever vigilant to help them to find their directions.
Pole stars are those stars which are used by the mariners to keep their ships in their proper courses on the sea routes of both the hemispheres. We know this world is having two poles i.e. North Pole and South Pole. So, ancient astronomers were of same opinion in their contemporary time of using two prominent stars in two poles. Now in the North Pole, Polaris and in the South Pole, Crux is such star. A Pole star is approximately aligned with earth’s axis of rotation; that is, a star whose apparent position is one of the celestial poles.
Ancients’ mariners used Polaris to find the position of their ships, to ply ship in their definite directions. It has different name in different countries. In ancient India it was named Druva Tara. In Bangladesh also it is Druva Tara. It is derived from ancient Indian mythology. In Greece its ancient name was set, Typhon. In the mythology of Hawaii it is known as Kiopa’a, in Japan it is known as Myokan Bosatsu etc. Not only to ancient mariners but also ancient travellers of the North Pole took the help of this star to travel by night. It is worth mentioning here that big merchants’ caravans used to walk by night when they followed desert path. Today also to the soldiers of countries of northern hemisphere take the help of Polaris when they are in night mission or night march.
The pole star, Polaris is directly above the North Pole of the earth and stays there all the time. But to specialist Polaris is also moving but it is in such distance that open eye can’t trace it. Due to precession after long time another star will be seen in the present place of Polaris. This is due to spinning of the axis of the earth. This precession needs about 26000 years for one turn. To find Polaris mariners would take the help of two constellations as our soldiers do now.
Between those two constellations one was named the Great Bear or the Big Dipper and another one is Cassiopeia. The first one looks like a pan with a handle. Its end two stars are called pointers that point towards the Polaris. This constellation is seen in one side of the Polaris. In the other side of the above constellation is the natural place of Cassiopeia. This constellation is looks like W. So these are also named W stars. In between these two constellations one can see Polaris. When mariners or any one finds Polaris they are exactly look at the True north. Then they can find out their own position and can plot their course by other celestial or any other prominent figures in the shore like Light house, Hill top etc which are also in the charts. That they do by intersection, resection etc methods.
To set navigational fix in the southern hemisphere ancient mariners took the help of certain South star. But due to spinning of the axis of the earth after certain length of time nearby star replaces South star as in the case of Polaris. This process is precession. But now there is no south star which is as useful as Polaris of the northern hemisphere. However, now Southern Cross constellation functions as an approximate southern pole constellation. Its other name is ‘Crux’ constellation. At the equator it is possible to see both the Polaris and the Southern Cross.
Other prominent stars in the southern pole i.e. close to the south celestial pole are Sigma Octanis and Achernar. Sigma Octanis is the naked eyes star. But that is visible only in the clear night. So unusable for navigational purposes. In around 2800 BC Achernar was only 8 degrees from the South Pole. So the Southern Cross constellation is more logical for the present day mariners to find celestial south as it appears at the Southern Hemisphere. It can be found in the Milky Way near the Coal sack Nebula. In extension to the south it points onto the south celestial pole.
The Southern Cross is a special constellation because it is part of a bigger constellation called Centaurus. From the northern hemisphere it cannot be seen now. But the Greek in their Classical antiquity could watch it. For precession now they can see it. In the Greek mythology Chiron was transformed into constellation Centaurus by Zeus. There are many legends and also names of this constellation. To a German clan its name is ‘Yarandoo’for what there was also a legend. The ancient religious belief of Egyptians was: Crux was the place where the sun Goddess Horus was crucified.
Whatever the case may be Pole stars like ancient mariners will be helping future navigators of the earth also. Due to precession at that time other star may take place of present North and South stars. Crux the Southern Cross now is visible from Latitude 25 degree north and completely invisible in latitude above 35 degree north. Because of its cross shaped asterism it is commonly known as Southern Cross. Southern celestial pole can be located from the crux and its two pointers a Centuri and B centuri.
Crux constellation is the smallest of the 88 modern constellations. Latinized word of cross is crux. Its stars are Gamma Crucis, Delta Crucis, Epsilon Crucis, Mu Crucis.
From the very ancient time North Star and South Star were the guides of the mariners. Now Marine, Air and Space navigators are using sophisticated devices for the navigation of their crafts. Now scientists are planning for navigation in the space at the speed light. Some also is thinking about time travel. Scientists opined that travel at the speed of light may be possible in distant future but beyond the speed of light travel is not possible from the earth. However some also opined that may also be possible from other phenomenon of the universe which are not known till date to our thinkers. Travel to the past is not possible by us. But it is interesting that past is travelling us now and again. Even incidents of Big Bang are continuously visible at the distance where light of that incident reaches. Thus our observation devices everyday tracing incidents what occurred even Billions of years ago of what light reaches us in due time.
We can guess till the Doomsday even with the discovery of most sophisticated navigational devices importance of Pole Stars will remain to our mariners and soldiers but we do not know for our flight in the space during inter planetary travel will these be useful or if aliens come from other universes how will our pole stars help them? They will certainly have their own navigational system.
(Ref: Various entries of Wikipedia and training materials.)