The total or partial obscuring of one heavenly body by another; a passing into the shadow of a heavenly body.

An eclipse of the moon occurs when the earth is between the moon and the sun, thus depriving the moon of the sun's light. An eclipse of the sun occurs when the moon is between the sun and the earth.

Man has always regarded the sun with awe and reverence, not only because it is seen to be the energy source of all life, but also because of its constancy and the inflexible reliability of the cycle of day and night. This diurnal cycle has been built into the evolutionary pattern of all living things so that they respond to sunset and sunrise as if remotely controlled by the sun itself. Sunset and dawn have become the natural regulators of our activities and rest periods. It is not surprising, therefore, that the sun should be treated with respect and even worshipped, because of the security that it inspires. It is because of the unfaltering cycle of the movement of the sun across the sky that we are peculiarly sensitive to any interruption that occurs.

In the days when solar eclipses were not understood, these phenomena were the cause of great alarm and were generally ascribed to supernatural agency. Among the Romans at one time it was even considered blasphemous and held to be a legal offense to speak openly of their being due to natural causes. A total solar eclipse is indeed awe-inspiring even to experienced astronomers. The scene is set by the gradual weakening of the sunlight as the moon moves across the disc of the sun, even though the sky remains clear and blue. Just before the eclipse is total the shadow can be seen bearing down at a speed of about 2000 miles an hour and the air has become unusually still. As the darkness sweeps down there is an involuntary temptation to crouch and let the shadow pass; a glance at the sun reveals the crimson prominences, like huge angry flames embedded in the pearly light of the corona. One's attention is riveted on the magnificent spectacle until suddenly the sun reappears. Dawn is repeated in the space of a few seconds and the whole world seems to come to life again.

The earliest recorded eclipse seems to have been the one that took place on 22 October 2136 BC, which is referred to in the ancient Chinese classic the Chou King or Book of History. Eclipses must have been observed earlier than this for the story has it that the two official astronomers of the time were taken by surprise by this one, with the result that there was insufficient time to prepare the customary rites. The normal procedure was to beat drums and gongs, shoot arrows in the air, and make a general din with the intention of frightening away the monster that threatened to devour the sun. In spite of the fact that the sun recovered from this attack the two astronomers were executed for their negligence. There are many other cases of the use of various rites to ward off the threat to the sun.

One particularly interesting case in modern times is the one recorded in a letter to the Philadelphia Inquirer concerning the eclipse of 29 July 1878:
 

"It was the grandest sight I ever beheld but it frightened the Indians badly. Some of them threw themselves upon their knees and invoked the Divine blessing; others flung themselves flat on the ground, face downwards; others cried and yelled in frantic excitement and terror. Finally one old fellow stepped from the door of his lodge, pistol in hand, and fixing his eyes on the darkened sun, mumbled a few unintelligible words and raising his arm took direct aim at the luminary, fired off his pistol, and after throwing his arms about his head ins series of extraordinary gesticulations, retreated to his own quarters. As it happened, that very instant was the conclusion of totality."

Solar eclipses are usually very short and the total phase cannot last longer than eight minutes. It is this transient nature of the event that seems to promote the use of some sort of ritual. No sooner have the demonstrations begun than the monster moves away and the eclipse is over. Such highly 'effective' deterrents will obviously be remembered and used again if the occasion should arise.

Nowadays we expect eclipse predictions to be accurate to a fraction of a second because we understand the underlying physical principles and have studied the motions of the earth, the moon and the sun in great detail. In the story of the Chinese eclipse there is an inference that the astronomers should have known about it in advance and there is good reason for believing that crude predictions were possible in those days because of the repetitive cycle of eclipses known as the Saros.

The Babylonians discovered that there was a Saros or cycle of 223 intervals between new moons, after which eclipses of the sun and moon recur. If an eclipse is seen on a particular day, then it is certain that another will happen 18 years, 10 days and 7 hours later which may be visible from the same place but which will not have the same appearance. On average there are 41 eclipses in the Saros cycle, and each one of these will be followed by another just over 18 years later. The Saros was almost certainly known to the Chinese and they would have used it in predetermining the dates of eclipses. The first well documented example of the use of the Saros was the prediction of the eclipse of 28 May 585 BC by Thales of Miletus, the Greek scientist and statesman, but there can be no doubt that the method was used earlier than this.

Obviously the ability to predict was a powerful tool in the hands of the astrologers and their readings of the sky were variously correlated with natural disasters, deaths, wars and the displeasure of the gods.

In more recent times, others have used their knowledge of eclipses to great effect. Sir Arthur Helps, in his Life of Columbus (1910) relates the story of how the explorer used the lunar eclipse of 2 April 1493 to obtain provisions from the inhabitants of Jamaica. At first they were reluctant to help him and he threatened them with divine vengeance, 'for that very night the light of the Moon would fail'. The natives were frightened and during the eclipse they approached Columbus and implored his intercession — with the inevitable result that the moon was restored to them and provisioning ceased to be a problem.

The only difference between lunar and solar eclipses as far as prediction and observation are concerned is that a total solar eclipse can be seen only from a narrow strip on the earth's surface across which the moon's shadow sweeps during the time of the eclipse, and which may be only about 150 miles wide. Lunar eclipses can be seen from the entire moonward hemisphere of the earth.

One would expect that some detailed knowledge of the processes causing eclipses would dispel some of the fears accompanying them, but the evidence of modern anthropologists seems to refute this. It seems that the basic reaction to a major natural disturbance like an eclipse still contains a certain amount of fear.
 

Related videos:
-- Mystery of the Full Moon.
-- Nova - Eclipse of the Century.
-- Click HERE for more related videos.

Related books:
-- Eclipse: An Introduction to Total and Partial Eclipses of the Sun and Moon.
-- Eclipse!: The What, Where, When, Why, and How Guide to Watching Solar and Lunar Eclipses.
-- Eclipses: Nature's Blackouts (First Book).
-- The Cambridge Eclipse Photography Guide: How and Where to Observe and Photography Solar and Lunar Eclipses.
-- The Sun in Eclipse (Practical Astronomy).
-- Totality: Eclipses of the Sun.
-- Click HERE for more related books.

Further info:
Astronomy On-Line: Lunar Eclipses.
Index - Solar Eclipse: Links Page.
Solar Data Analysis Center Eclipse Information.
Solar Eclipse: Stories From the Path of Totality.