CELESTIAL NAVIGATION

Ever wonder how the earlier mariners sailed around the world, discovered new territories and yet able to return home without being lost. Here's the answer.

CELESTIAL NAVIGATION

Since time immemorial, human race has been finding their way from the heaven, following the heavenly bodies that never fail to appear at the onset of darkness. Many of the stars have Arabic names because the people of the desert used them for direction and later on did the mariners across the sea and ocean. Celestial Navigation is the art as well as a science of navigating by the stars, sun, moon and planets. Of course, with the inventions of electronic and radio, it loses its importance. More so today, the uses of GPS from satellites have assigned this form of navigation to history.

The concept

The stars are very distant from the earth. As a result it appeared constant and can be spotted at the same place every night. Just like the sun, we know where it will rise and the inclination at a certain time. But as the season changes, some shifts can be expected. As time changes, so do the inclination from the earth. In another word, one can predict that a certain star almost accurately its bearing and inclination at a specified time. Astronomers and mathematicians thus were able to work out a table to infer position from the bearing, inclination and times of the stars. The tables are call the ‘nautical almanac’ and ‘sight reduction table’.

Shooting the stars

Before we used the marine sextant to measure the inclinations of selected stars, one has to do his homework to find out what stars were visible from the ship's position together with the anticipated bearing(azimuth) and inclination(altitude). Good choice should be stars that were easily recognised and shots taken from different directions of the ship. Mariners were limited to dawn and twilight to take shots. At these times, both the horizon and only the brightest of star become visible and identifiable. The sextants measure the altitudes of the stars from the horizon. Precision timing to the nearest second must be noted at the time the ‘shot’ was taken. 3 stars altitudes were needed to get a ‘fix’ or position. Of course, the moon, planets and the sun at noon where it was at its highest point were also used to obtain position lines.

Plotting the position.

Once the readings were taken, it’s back to the chart table to complete a complex set of calculations to determine position lines. Initially we were completely lost when we can’t even get one position line to plot on the chart. As time went by, we improved and learned from mistakes. Till this day, I still remembered a quotation on the nautical almanac. It read, “MAN IS NEVER LOST, ONLY TEMPORARILY MISPLACED”. It has since been adopted as my personal life philosophy.

Meridian Passage.

The aim is to find the sun highest altitude at around noon. After a set of calculation, a mariner can now determine the ship latitude. In layman term, how far is the ship away from the equator.

My greatest respect for the ancient mariner

Having gone through this training, I now realised how brave and courageous the ancient mariners were. Depending only on wind to sail with compass, inaccurate sextants, and rudimentary tables, they were able to navigate around the world. Of course many were lost and shipwrecked. Nevertheless, thesa pioneera were precursors to modern day electronic navigators like the INS and GPS. First the sailing yacht, the steam engines and then the diesel engines and eventually modern aviation. Without the knowledge of navigation, we could never find our destinations across the ocean and the land mass.




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