The Eclipse

The Beauty of an Eclipse

1. Introduction

The older responses to eclipses appear to have been that they were a disruption of the natural order of things, especially in the case of solar eclipses. This is understandable since solar eclipses occur when the light from the Sun is suddenly cut off. It was one thing when it became dark after the setting of the Sun, but when the Sun was shining and then darkness reigned, it was cause for alarm. In ancient China, it was believed that solar eclipses occurred when a dragon devoured the Sun. The ancient Egyptians and Greeks believed that the events were ill omens, and wars being fought at the time of an eclipse are said to have been stopped. In more recent centuries, there have been records of witnesses to an eclipse becoming frightened or running to get indoors. One of the most famous recent events was during the War of 1812 when a group of Native Americans at Fort Mims in Alabama were frightened by a solar eclipse and as a result, this prevented them from attacking the fort. In many primitive cultures, eclipses are still seen as bad omens. In India, for example, it is still a widely held belief that food cooked before an eclipse is rendered impure and unfit to eat.

An eclipse is a phenomenon that occurs when the light or view of one celestial body is blocked by another. The term eclipse is most often used to describe either a solar eclipse, when the Moon's shadow crosses the Earth's surface, or a lunar eclipse, when the Moon moves into the Earth's shadow. However, it can also refer to such events beyond the Earth-Moon system: for example, a planet moving into the shadow cast by one of its moons, a moon passing into the shadow cast by its parent planet, or a moon passing into the shadow of another moon. A solar eclipse of some sort occurs on average every 18 months. The period is shorter for lunar eclipses, with at least two per year. Eclipses occur only when the Sun, Earth, and Moon are all in a straight line (termed "syzygy"). A syzygy only results in an eclipse about once every six months, because the orbital planes of the Moon and Sun differ. Eclipses have been observed by humanity for much of its history. The human response to an eclipse has been both awe and fear.

1.1. Definition of an Eclipse

The word eclipse is derived from the ancient Greek ekleipsis, gender of ekleiptein, which means to abandon, take away, or fail. An eclipse is a rare and unusual event in nature. It is very exciting to be able to observe one of nature's most dramatic events - a solar eclipse. More exciting is to be able to research why they occur. There was a time when a solar eclipse was considered a bad omen, a portent of doom. People were flabbergasted. Today, a solar eclipse is a celebration of a delightful coincidence. When the moon exactly covers the sun, it seems to fit perfectly. The sun's size and the moon's size are coincidentally the same to make the sun just barely visible around the moon, which in turn creates a ring effect. This delightful coincidence has a profound effect on those who are fortunate enough to view an eclipse.

Eclipses belong to a family of phenomena known as syzygies. The word syzygy has different meanings when used in different scientific contexts. In the context of eclipses, it refers to a straight-line configuration of three celestial bodies in a gravitational system. By a coincidence of nearly perfect geometry, the relative sizes and distances of the moon and the sun.

1.2. Importance of Studying Eclipses

But what are the specific reasons for studying eclipses in this day and age? Solar eclipses can only occur at New Moon, when the Moon passes between the Earth and Sun. During a solar eclipse, some part of the Earth will pass through the penumbra and experience a partial eclipse, and a small area will be completely shadowed by the Moon and experience a total eclipse. (The maximum duration for a total solar eclipse is 7m32s). Considering that the occurrence of New Moons and the position of the Moon's orbit about the Earth give simple, specific criteria for when solar eclipses can occur, it is surprising that the details of the occurrence and paths of solar eclipses are not more widely understood. By observation, photographing or recording the timing and direction of the shadow bands on the Earth at the time of a total solar eclipse, it is possible to determine the irregularities in the Moon's motion or the changes in the Earth's rotation, which might affect the occurrence and prediction of solar eclipses. A very precise record of the times and positions of total eclipses around the world allows further testing of the consistency of astronomical constants, such as the solar mass, or the general relativistic parameters. By comparing detailed eclipse observations and eclipse predictions in this manner, it is possible to improve our knowledge of the structure, position, and the motions of the Earth, Moon, and the Sun, and develop our understanding of fundamental physics. Finally, solar eclipses provide a rare opportunity to observe the solar corona and prominences around the dark disk of the Moon, without the need for space-based instruments. This has been historically important for solar physics, and recent studies of eclipse-acquired data are still proving to be significant.

The reason we study eclipses and make predictions concerning when and where they will be visible is because they can be spectacular, beautiful events. They are also genuinely interesting astronomical phenomena that provide opportunities to investigate the behavior of the Sun and the Moon using relatively simple equipment. Eclipses have been observed for centuries and are a prominent feature in many cultural and historical records. They were also of historical significance, particularly in the case of solar eclipses, before we fully understood the astronomical reasons for their occurrence. Eclipse predictions have been used to verify the historical accuracy of certain ancient records. One famous example is the record of an ancient solar eclipse in China, described in the historical text the Ch'un-ch'iu, which some modern historians believe was an event in 1302 BC. Calculations show that an eclipse was indeed visible in the right place (China) in 1302 BC, so it is possible that this record is the oldest known solar eclipse observation in human history. Eclipses offer an opportunity for astronomers to engage with the public, to demonstrate astronomy in action as they observe and measure these events, and possibly reveal some of their findings to an audience.