Star Gazers and Navigation

STAR-GAZERS,       MATHEMATICIANS ,  AND  NAVIGATION

(Please click on the images for larger and higher res reproductions)

Navigation is about finding one’s way around the Earth, and travelling safely and economically from one point to another.  The word is derived from the Latin ‘navis’ (ship) and agere (to drive),  and was applied to the theoretical and practical skill of planning sea voyages, and managing and steering ships.

I first became fascinated by the Science of Navigation when I served in the Australian Merchant Navy aboard the Burns Philp cargo-passenger ship – MV Malaita.  Her captain, at the time, was Brett Hilder – one of the most famous ‘navigators’ of the Pacific South Seas, who – years before – had been at sea with my father. Even today you’ll find his name of some of the charts still in use in the South Pacific.  Malaita was famous in the area: she had survived being torpedoed whilst evacuating Port Moresby in New Guinea as the Japanese invaded from the north, and her bar was always packed with visitors when we were in port. My time and life aboard Malaita taught me much, and I always keep a photo of her near me.

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I took this photo of MV Malaita when she was alongside the wharf in Madang, on the northern coast of New Guinea. Copyright photo.

The skill of Navigation is much older than the word and – over the centuries – has evolved into a science and technology that now controls the movements of ships, aircraft, and spacecraft.  Today the seaman, airman, astronaut, and even the driver of modern cars needs only push a few buttons for his satellite Global Positioning System (GPS) to tell him his exact position, speed (over the ground or through air or water), course, and distance run and still to run.

Yet only a few years ago navigation involved finding one’s position by observations of the celestial bodies, dead reckoning (the track kept of a ship’s course and speed, allowing for wind, drift, currents and so on, when celestial observations were impossible), astronomical tables, and a reliable chronometer.

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Celestial Bodies: Venus and Jupiter photographed near the Gardjola in Senglea, Malta.

In Columbus’ day a mariner could rely only on finding his latitude – his position north or south of the equator – by observing the greatest angle of the sun above the horizon at noon, and applying the astronomical calculation to this figure.

As far as we know Columbus made only three attempts to find his latitude as he crossed the Atlantic for the first time – and he got it wrong each time.  He had no hope of finding his longitude – his  position now reckoned east or west of the ‘Prime Meridian’ at Greenwich – because calculations of longitude rely on accurate time-keeping by marine chronometers: an instrument developed by John Harrison between 1728 and 1762.  One degree of longitude is 15 minutes of time.

The accuracy of celestial observations depended on the mariner’s skill with his instruments, the accuracy of his chronometer, and the accuracy of his mathematical calculations with reference to astronomical tables of the positions and movements of the celestial bodies.

The first of these astronomical tables was the Almagest or ‘Great Treatise’, an astronomical and mathematical encyclopaedia by Ptolemy (Claudius Ptolemaeus) of Alexandria around AD 150.  This 13-volume work was the guide among all Arab and European astronomers until the beginning of the 17th century.  It was translated into Arabic in 827, and into Latin in the 12th century.

In his Almagest, Ptolemy drew on the work of the great Rhodean astronomer and mathematician, Hipparchus, who died around 127 BC. Hipparchus, who calculated the length of the year to within 6.5 minutes, compiled the first known Star Catalogue around 129 BC.  This listed some 850 stars,and gave their brightness expressed in six magnitudes, as we know them today.

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The Ptolomaic System of the Universe with the Earth at its centre.

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This is a 15th century copy, redrawn from Ptolemy’s ‘Geography’ – showing his World Map of 150 AD (CE) (Image in the Public Domain.)

Ancient scientists had agreed on a spherical Earth since the 6th or 5th century BC, but disagreed on whether the Earth or the Sun was the central point around which the other celestial bodies revolved.  We had to wait until the 15th century AD, and the work of Cusa, Copernicus, and Galileo, before regular observations over long periods proved that the Sun was the central point.

Even then, and ignoring the evidence, the Church persisted in its dogma of a flat earth, and the earth as the centre of what we now call the Solar System.  The Church had problems with ‘Heavenly Bodies’,  and the Holy Office – the  Inquisition set up by St Dominic- had scientists and mathematicians tortured and  burned alive for their heresy denying and contradicting the teachings of the Church.

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Galileo with his telescope in St Mark’s Square, Venice looking at and ‘discovering’ the four moons of Jupiter in 1611. Galileo did not, in fact, invent the telescope. A man from the Netherlands – Hans Lippershey – invented it in 1608, and Galileo studied the idea and developed a more powerful telescope of his own.  (Image in the public domain and courtesy of Wikimedia.)

Galileo, however, great and revelatory as his discoveries were, was following in the footsteps of many great astronomers and scientists before him. Working around 150 BC, Hipparchus was probably the first person to use instruments to measure accurately the positions and movements of the celestial bodies.  Yet, as far as we know, no astronomical instruments were used in the great monolithic structures such as Stonehenge in England (built in 2500 to 1700 BC); the Ziggurats of Babylonia of the same period – from the tops of which astrologer-priests observed the motions of the Sun, Moon, and planets – nor in the siting and building of the far older Neolithic temples found on Malta.

Nor were astronomical instruments used in ancient Egypt, pre-Columbian Mexico, or ancient China.  Here, calendrical human eye observations were used to predict eclipses, the equinoxes, and dry and rainy seasons.  Although much later, the Mayan calendar can be traced to the mountains of central Mexico where, some 2,500 years ago, Zapotec Indians levelled a mountain-top to build a citadel on Mount Alban.  The Mount Alban Calendar of 433 BC is claimed to be as accurate as our modern Gregorian calendar.

The Dresden Codex, so called because it was acquired by the Saxon State Library in Dresden, is one of several pre-Columbian Mayan hieroglyphic works that survived book-burning by the fanatical Spanish Christian clergy.  Its calculations, including predictions of eclipses and the synodical period of Venus, are extremely accurate, and the Maya’s reputation,  as astronomers, is based – largely – on these calculations.

More than 1,000 years ago, the Chinese Imperial Observatory employed 300 astronomers to compile complex calendars, but Chinese astronomical records date from more then 3,000 years ago.  From these records,modern astronomers learned of the appearance of ancient comets and meteor showers, and the movement of celestial bodies. \they applied this knowledge to modern astronomical problems.

In modern Beijing, we can still see and walk around one of the oldest observatories in the world, built in 1452 AD.  Here are huge astronomic instruments mounted on a platform and attached to the building. Recently, the government restored the observatory and its instruments.

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The observatory in Beijing, photographed in 1874. (Image in the Public Domain)

Yet the predecessors of truly modern observatories were those built in the Islamic world: at Damascus and Baghdad as early as the 9th and 10th centuries AD.  Muhammed Ibn Musa Al-Khawarizmi, the Muslim mathematician and astronomer who lived and worked in Baghdad from 780 to 860 AD, introduced Hindu-Arabic numerals, the decimal or base-10 system, and the concepts of algebra in European mathematics.  (The word ‘algebra’ is derived from the Arabic al-jabr, one of the 99 names of Allah.

The decimal system, which included the use of the zero as a numeral, was spread throughout Europe in the 10th century by Gerbert, who later became Pope Sylvester II.  The development and widespread use of this system allowed much greater ease and accuracy in the calculations required in astronomy and navigation. Ultimately, it led to greater efficiency in handling data, the understanding and use of logarithms and slide rules, and the development of mechanical and electronic calculators and computers.

Another famous Islamic observatory and seat of learning was founded at Maragheh around 1260 AD.  Here, substantial modifications were made to Ptolemaic astronomy.  The most productive Islamic observatory was built by Ulugh Beg at Samarkand around 1320 AD.  He and his assistants made a new catalogue of stars from observations recorded with a large quadrant.

In 1576 on the Danish island of Hven, the first important working observatory in Europe was built for Tycho Brahe by King Frederick of Denmark.  The first optical telescope used to study the heavens was built by Galileo Galilei in 1609.

In England, King Charles II founded the Royal Observatory in 1675, and its functions were to be in practical astronomy – navigation,time-keeping, determining star positions, and publishing almanacs.  Here, John Flamsteed, the first Astronomer Royal of England, compiled a new and extraordinarily accurate star catalogue, Historia Celestis Britannica, in which he listed more than 3,000 stars.

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The Royal Observatory at Greenwich 1676. Engraved by Francis Place. (Image in Public Domain.)

The Royal Greenwich Observatory published its first Nautical Almanacin 1767, based on the longitude of Greenwich.  This set of tables proved so popular that it led, in part, to the adoption – in 1844 – of the Greenwich meridian as the Earth’s Prime Meridian, and the starting point of international time zones.

Modern radio telescopes can observe most wavelengths from a few millimetres to 20 metres, and can obtain high resolution images of cosmic radio sources. Spaceage technology has placed astronomical instruments above the absorbing and distorting atmosphere of the Earth, and enabled astronomers to build radio telescopes sensitive to electromagnetic spectra apart from the visible light and radio waves.

These new instruments have been built to observe gamma rays, X rays, and ultraviolet and infra-red radiation. The Hubble Space Telescope, for instance, has enabled astronomers to see to the visible limits of our universe, taking us back in time some 12 to 13.5 billion years.

Man’s imagination, curiosity and speculation led to this extraordinary story of achievements; of burgeoning knowledge and understanding that brought us far from the darkness of superstition.  Yet the mystery of the Universe remains, and it still inspires us.

At sea, or in the mountains – wherever we can escape the pollution of our cities – we can still stand and look up in starry-eyed wonder at the infinite splendour – and magnitude – of the Universe.

Copyright: Rob Weatherburn 2015