Eclipse: The Celestial Phenomenon That Changed the Course of History
Duncan Steel
Language: English
Pages: 492
ISBN: 030907438X
Format: PDF / Kindle (mobi) / ePub
Whether interpreted as an auspicious omen or a sentinel of doom, eclipses have had a profound effect upon our cultural development. Throughout recorded history, they have evoked consternation, fear, and dreadâ€"as well as awe and wonderment.
Ancient peoples were clearly disconcerted by them. The Romans marked pivotal battles with the Greeks by references to an eclipse. The date of the crucifixion of Jesus Christ has been derived by using biblical mentions of an eclipse. Perhaps most famously, Christopher Columbus extorted much-needed foodstuffs from some increasingly unfriendly native hosts by purporting to demonstrate the wrath of his most powerful God when he accurately predicted a lunar eclipse.
The pattern that eclipses followâ€"a cycle, called the sarosâ€"was actually calculated thousands of years ago. However, it is only with the help of modern computers that we have been able to analyze and appreciate the data. Eclipses provide unique opportunities for today’s scientists to study such contrasting phenomena as the upper layers of the sun, the slowdown of our planet’s spin rate, and the effects of celestial events on human psychology.
In Eclipse, Duncan Steel expertly captures our continuing fascination with all manner of eclipsesâ€"including the familiar solar and lunar varieties and other kinds involving stars, planets, asteroids, and comets as well as distant galaxies and quasars. Steel helps us see that, in astronomical terms, eclipses are really rather straightforward affairs. Moving beyond the mysticism and the magic, the science of eclipses is revealed.
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each other. Historically, solar eclipses have provided ideal opportunities for scientists to study a range of phenomena besides the spectacular corona. For example, by timing the exact moment of transit, the Moon’s position can be measured to very high precision. Although the Moon orbits the Earth in a roughly elliptical path, there are small variations, such as a very gradual drift away from Earth. It is important for astronomers and geophysicists to understand these corrections. Today, better
occur is fine, but getting a total solar eclipse right is another thing entirely. On balance it seems that Thales and his contemporaries did not know how to foresee eclipses by any means other than the short-term relations like the ten-day shifts from one year to the next. Hipparchus used eclipse data, and the saronic cycle, to ascertain accurate values for the year and the lunar months, but did not make forward eclipse predictions. The eclipse knowledge gathered by the Babylonians lay dormant
May when the Sun is passing through the constellation Taurus, and crossing a rich cluster of bright stars known as the Hyades. His mentor, the Astronomer Royal Sir Frank Dyson, was so enthused about the concept that he lobbied the government to avoid having the youthful Eddington drafted to fight in the First World War. Instead Eddington was allowed to prepare for the great eclipse expedition of 1919. The British foray was in several parts, with Eddington leading one group to Principe (a tiny
the rotation rate of the planet is also found to undergo seasonal variations, as the atmosphere swells under summer heating and then shrinks in the winter. It is because of this general slowing down of the Earth that leap seconds need to be inserted into some years. In the past, time was defined astronomically, from observations of when the Sun and the stars crossed the noon meridian. However, during the twentieth century methods of time determination that were of ever increasing accuracy were
RECEDING As the Earth’s speed of rotation diminishes owing to tidal friction, its angular momentum falls.The angular momentum of a body is a measure of its disinclination to stop rotating (or indeed to speed up), whether that rotation is in the form of spinning on its axis, or revolving around another body. An example of the latter is any planet orbiting the Sun, or the Moon orbiting the Earth. A body’s 152 / ECLIPSE angular momentum depends upon its total mass, the distribution of that mass,
