Historical view

Babylon

The origins of Babylonian astronomy is discussed by Pederson (1987) who says that the Babylonian people celestial objects were important religious identities, with the sun, moon and planets being identified as their superior gods. They used it in the creation and maintenance of the calendar. This task was also assigned to the astronomers who would fix the first day of the month. This was when the new moon was first visible (Pannekoek, 1961). From this they were able to divide the year into twelve months, with the occasional thirteenth added.    

 

The high point of Babylonian astronomy can be seen from the Chaldean Tables. The tables are divided in two, lunar and planetary. The tables are unique for they give the position of celestial objects in longitude and latitude. Pannekoek (1961) also explores the achievements in the tables. Including the representation of planets motion on a zig zag line. As well as the determination of the longitude of Jupiter which has an error in excess of 1°30´.

 

Greece

The ancient Greek astronomers were also philosophers interested in the universe and how everything in it is governed. Greek astronomers would speculate on the size and shape of the universe.

Thales saw the earth as a flat round disk surrounded by ocean, while Anaximander believed the earth to be a “…cylindrical drum, suspended in the middle of a vast space where it remains at rest ‘because it is the same distance from everything’.” (Pederson, 1987, p.65).

Aristarchus of Samos introduced the idea of a heliocentric model of the universe, theorising “…that the fixed stars and the sun remain motionless, that the earth revolves around the sun in the circumference or a circle…” (Health, 1932, p.106).

While Hipparchus introduced trigonometric applications to astronomical calculations in his “Table of Chords”. Ptolemy’s “Almagest” was the most comprehensive text on astronomy when completed. Book VIII of “Almagest” contains a catalogue of stars which lists the positions of stars, given as ecliptic coordinates (Neugebauer, 1975). Some of the instruments available to Greek astronomers include globes, quadrants, armillary spheres and astrolabes.

 

India

Shukla (1987) classifies Indian astronomy into two categories vedic and post vedic astronomy. During the vedic the aim of the astronomical observations as “It centred round the Sun and Moon and its aim was to study the natural divisions of times caused by the motion of the Sun and Moon, such as days, months, seasons and years…” (Shukla, 1987, p.9). The post vedic astronomy saw the introduction of study into the five known planets. The development of their understanding grows from the initial stages of synodic motion, noting “…the times of first and last visibility, the duration of their appearance and disappearance, the distance from the Sun at the time of their first and last visibility, the times of their retrograde motion…” (Shulka, 1987, p.14).

Some of the instruments that were available to the Indian astronomers include the sundial. A good example is the Great Samrat Yantra which could measure local time and the declination and right ascension of celestial objects (Ohashi, 1987) . Determination of time using the Great Samrat Yantra has been achieved to a precision of between ±10 and ±90 seconds, and a precision between ±1 minute and ±15 minutes of arc for declination and a similar range for right ascension (Sharma, 1995).

 

Arabia

Arabic astronomers were greatly influenced by the works of Ptolemy and in particular his great treatise, the “Almagest”. With its translation into Arabic they were able to study the text and came to hold it in high regard, using it as the basis for their own astronomy.

However the Arabian astronomers were not just followers of Ptolemy astronomy, they were also independent thinkers. Saliba (2007, p.132) explains some of the problems that faced Arabian astronomers. “The serious astronomers had to answer more complex questions regarding the suitability of the proposed Ptolemaic astronomical configurations in accounting for the observations on the one hand, and in embodying the prevailing cosmological system of Aristotle on the other.”

The astrolabe was one of the most important astronomical instruments used by Arab astronomers. Turner (1997) identifies the astrolabe as “...the most important computational instrument of the Middle Ages and early Renaissance...” (p.66).

 

Europe and the Scientific Revolution

The scientific revolution that occurred in Europe during the Middle Ages is a major step in the development of astronomy to a level not previously known. This began with the introduction of the translated manuscripts from ancient Greece into Western Europe, with the work of Ptolemy making the greatest impact. At the beginning of the new astronomical age in Europe two ways were open for the study of astronomy (Pannekoek, 1961, p.179) “(i) the collecting and studying of incorrupt manuscripts of the ancients and, (ii) the making of new observations”.

The influence of famous astronomers Copernicus’s ‘Commentariolus’ and his reintroduction of the heliocentric theory, Tycho Brahe and his naked eye instruments, Galileo’s theory of falling bodies and mechanics, Kepler’s laws governing the motion of the planets around the sun and Newton’s “Principia” as fundamentally important in the development of astronomy. Harrisons H1 had a major influence on positional astronomy. It provided navigators with an easy and convenient way to transfer the time of the prime meridian through their travels and compare this to the local meridian, allowing them to determine their longitude.

POSITIONAL ASTRONOMEY THROUGH THE AGES

BY

BENJAMIN JACKSON

Last Update 29/10/2008