Development of Cometary Thought

PART - I

Subodh Mahanti

The development of the scientific understanding about comets has a long and intriguing history. For centuries people (common people and scientists alike) have pondered the appearance of these mysterious apparitions. People's fascination for them, as seneca pointed out, was because they were unusual strange phenomena. They appear rarely. Before the seventeenth century comets were not considered as celestial bodies but as signals at a sinful Earth from God. celichius as quoted above was no doubt expressing the majority view of the comet prevalent in the 16th century. of course, there were opponents, though their number were few. for example Andreas Dudith (1533-89), the Hungarian scholar, countered celichius views by stating that if comets were caused by the sins of the mortals then they would never be absent from the sky.

Aristotle (384-322 BC), whose importance in the history of western thought cannot be exaggerated, dominated almost every aspects of western thought for nearly 2000 years. Aristotle documented his cometary ideas in his book, Meteorologica, which dealt with the sublunar or terrestrial world. Besides stating his own views Aristotle presented the views of his Greek predecessors from the sixth to the fourth century BC including those of Pythagoras (c.560-480B-C), Hippocrates of Chios (fl.440B.C.) and Anaxagoras of Clazomenae (c.500-428B.C.). According to Aristotle the Pythagoreans believed in the existence of only one comet. Further they believed that it was a planet, which appeared infrequently and like Mercury it rose only a little above the horizon. Hippocrates like pythagoreans believed in the concept of a single comet. According to Hippocrates a comet's tail was formed when the comet drew up moisture from the earth below and it appeared at greater intervals than other stars, as it was slowest to move clear of the sun. Aristotle described in his Meteorologica that according to Anaxagoras, comets were caused by planetary conjunction. Though Aristotle dismissed the idea by noting that comets were formed in regions of the sky where no planets travel it remained popular well into the seventeenth century.

To understand Aristotle's own ideas about comet we must have some idea about Aristotelian cosmology. Aristotle viewed the universe as finite spherical and geocentric where the first four elements viz. earth, water, air and fire moved naturally along straight, finite lines but they remained confined to the imperfect sublunar world. A fifth element or essence, Quintessence, permeated the supralunar space where the planets, Moon and the stars moved eternally in perfect circles. Aristotle placed the four concentric spheres in the following order _ the earth, the watery sphere, the airy sphere and the fiery sphere. According to Aristotle comet formed from the dry, warm exhalation emanated from the earth as the result of the Earth being heated by the Sun or planets. The cooler moisture also evaporated but it remained in the lower region. Only the warm, dry, windily exhalation rose upwards but at the border of the fiery sphere, the friction of their motion ignited them and resulted in comet. The resultant comet alongwith neighboring dry exhalation was carried about the Earth by the circular motion of the heavens in the fifth sphere. The form of the comet and how long it would sustain would depend on the comet and form of the exhalation. Aristotle's views on the nature of comets survived for two thousands years. Today we know that they have proved to be wrong. But it is worthwhile to note that Aristotle's cometary theories were physical and not metaphysical in nature. There was no place for superstition .

Like the Metereologica of Aristotle, the Natural Questions of Seneca is an important source of the earliest ideas about comets. It is from Seneca's Natural Questions we know the views of comets of the Chaldeans or Babylonians. From Seneca we also learn the cometary ideas of some Greek scholars like Ephorus of Cyme (fl. 340 BC), Epigenes, Apollonius of Myndus and Posidonius (135-51 BC). Ephorus had observed the splitting of a comet into two separate pieces and this enraged Seneca to ridicule him. But now we know many instances where comets have split. Epigenes' cometary ideas were modified version of Aristotelian ideas. According to Apollonius comets were neither illusions nor the results of planetary conjunctions.

While writing about comet Pliny has not taken note of the views of his contemporaries. He took comets as portent. He made them `terrifying apparitions' by describing in detail the disasters that followed a few cometary returns. He even formulated certain rules for predicting the nature of disaster that would follow a particular cometary appearance. Pliny noted that while some comets move but others do not. They could appear in any directions but those in the south had no tails.

Pliny developed a system of classification of comets and as noted by yeomans he described 10 types comets.

1. Pogonias - comets with a beard or mane hanging down from the lower part.

2. Acontias - vibrating like a javelin with very quick motion.

3. Xiphias - start and pointed like dagger.

4. Disceus - like a quoid or disceus amber, in colour

5. Pitheus - figure of a cask and emitting a smoky light .

6. Ceratias - appearance of a horn.

7. Lanpadias - appearing as burning torch.

8. Hippens - like a horse's mouth in rapid motion.

9. Argenteus - silver in colour, so bright that it is difficult to look at.

10. Hircus : goat comets ringed with coloud resembling tufts of hair.

Pliny's natural History was so popular that even in the late seventeenth century of the cometary types described by Pliny could be recognised in serious scientific works.

Ptolemy or Claudius Ptolemaeus (c AD 100-175) was considered a dominant scientific authority until the seventeenth century. We virtually know nothing about Ptolemy's life except that he lived and worked in Alexandria. Ptolemy did not describe about comets in his celebrated Almagest in which he treated the motion of heavenly bodies. This is because Ptolemy did not consider comets as heavenly bodies, rather he considered them as portent of evils. He described about comets in his work on astrology, the Tetrabiblos - a companion volume of the Almagest. While describing about the astrological implications of comets, he had even surpassed Pliny.

According to Ptolemy the part of the world to be affected by a comet could be guessed from the part of the sky in which the comet first appeared and the direction of its tail. The kind of disaster and the persons to be affected can be guessed from the shape of the comet. The comet's position with respect to the Sun would decided when disaster would strike. Disaster would strike soon if the comet appears near the rising Sun but if it appears in the west the disaster is delayed. Because of Ptolemy's unassailable influence many astrological work were incorrectly attributed to Ptolemy in the Middle Age. One such work titled Karpos or Centiloquy laid down specific rules for predicting comet related disasters. This work which often accompanied the Tetrabiblos in medieval Latin manuscripts. These two manuscripts were used for centuries to correlate appearances and disaster. Throughout the middle ages and also in renaissance times most of the writers on comets did not deviate from Aristotelian origin of comets and its astrological implications highlighted by Ptolemy.

Johannes Muller Michael Mastin

Albertus Magnus (1193-1280), the German philosopher and cleric and who was known as Doctor Universalis. considered comet as a coarse, terrestrial vapour originated from the lowest region of the airy sphere. The vapour in the course of his upward movement when rises to concare surface of the fiery sphere is ignited and people see it as a comet. It remain visible till the fuel supple lasts. His pupil Thomas Aquinas (C.1225-1274) heightened the fear of comet by stating that cometes were among the 15 signs preceding the God's coming to judgement . Rogar Bacon (1214-94) also a student of Albert Magnus and who played a pioneering role in the advancement of science, thought comet as portent and his ideas of comet had more to do with contemporary superstition the with scientific method. Martin Luther (1483-1546) referred comets as harlot stars and works of the devil.

up to the end of fourteenth century the ancient Chinese astronomers were ahead of their European counterparts. They were aware of the antisolar nature of a comet's tail as evident Li chung-feng recorded from description depicted in the history of the Chin Dynasty (AD 265-419), which was completed in AD 635.

"Among ominous stars the first are the hui-xing, commonly known as broom stars. The body is sort of star while the tail resembles a broom. Small comets measures several inches in length, but the larger ones may extend across the entire heaves. The appearance of a comet predicts military activities and great floods. brooms govern the sweeping away of old things and the assimilation of the new. A comet can appear in any one of the five colours, depending on the essence of that one of the five elements which has given birth to it.

According to the official astronomers, the body of the comet itself is non-luminous but derives its light from the Sun. So that when it appears in the evening it points toward the east while in the morning it points toward the west. It is south or north of the Sun, its tail always points following the same direction as the light of the Sun then suddenly it fades. The length of the rays is a measure of the calamity forefold by the comet."

While the disintegration of the Roman Empire the importance of the knowledge of the Greek language diminished. As a result the widespread knowledge of the early Greek sciences gradually disappeared. Only in the twelfth century Latin translations of early Greek works on science became widely available. The church dominated the European thought in the medieval period. It was the age of superstition for everything people looked back. So in case of comets the ideas were mostly derived from Aristotle and Ptolemi . The cometary views during 1200 to 1577 (when a great comet appear and which was scientifically observed by many well known astronomers of the day including Tycho Brahe) was dominated by superstition astrological considerations. But there were very few observers who attempted, may be hesitatingly, to study comments scientifically. One of them was Palo Toscanelli 1397 -1482), the Florentine astronomer and physician, was one of them. He made detailed observations (both descriptive and positional) of six comets that appear the 15th century (1433, 1449-1450,1456 (Halley), 1457 I, 1457 II and 1472 unfortunately his observation remained unknown till 1864 when Giovonni celoria, Director of Millan Astronomical observatory successful used them to compute the orbits of the comets.

George von Peurbach or Purbach (1423-61), the Austrian astronomer and mathematician, had tried a cometary parallax determination as early as 1456 but that time the techniques and instruments were not accurate enough to confirm whether comets were terrestrial or celestial phenomenon. However, it was Regiomontanus or Johanes Muller (1436) was also student of Peurabacho) is student generally given the credit for devising the techniques required for cometary parallax determination. It was in 1577 the comet's position was put beyond the moon by Michael Mastlin (1530-1631) Tycho Brahe (1546-1601) and Cornelius Gemma (1535-79). They all came to this conclusion after parallax measurement of the great comet of 1577.

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