posted 11-20-2015 02:29 PM
This rapidly paced manual in the Haynes series reviews how our understanding of the Moon has developed.The story starts with a brief account of how science and in particular astronomy were studied in classical times. The dominant figure was the philosopher Aristotle, who stated that Earth was located at the centre of the universe and that objects in the celestial realm pursued uniform and circular motions.
Very little further progress was made until the Renaissance. Nicolaus Copernicus showed that instead of the Sun daily revolving around Earth, Earth travels around the Sun on an annual basis. Later, the advent of the telescope enabled Galileo Galilei to discover the Moon to be a world possessing a vivid landscape.
Next Johannes Kepler realised the orbits of the planets and their satellites aren't circles but ellipses. This enabled him to develop three laws of planetary motion.
Along with an apple, the Moon played a key role in Isaac Newton's discovery of gravitation. In concert with three laws of motion that define the nature of physical systems, gravitation explained Kepler's empirical laws.
It was hoped that knowledge of the motion of the Moon across the sky and the character of its surface of would provide a way to determine the longitude of a ship at sea. New telescopes enabled people to map the Moon with ever increasing sophistication, and photographic atlases were produced in the late 19th century. But studies revealed irregularities in the motion of the Moon that made using it as a clock impracticable. On the other hand, by then the 'longitude problem' had been solved by the invention of the marine chronometer.
However, by then the Moon had become an object of fascination in its own right. In addition to mapping the Moon, people gave thought to the process that had created its distinctive surface features. Arguments raged about whether the process involved volcanism or the impact of celestial objects such as wayward asteroids.
As astronomers investigated ever finer details of the lunar surface, the Moon attracted the interest of geologists, whose insights revealed the history of that world in ways never imagined by astronomers. In general, however, astronomers resented this intrusion into their bailiwick.
In the mid-20th century we developed the means to send automated probes to investigate the Moon by going into orbit around it and by landing on its surface.
As astronauts prepared to make the first human landing on the Moon, scientists continued to argue about what they would find there.
The 'ground truth' provided by the samples returned by the early landings supported some hypotheses and shot down others.
Later missions were field trips designed to understand specific aspects of the nature of the lunar surface and its history.
There was then a considerable pause as the results from this incredible early period of lunar astronautics were assessed and consolidated. One result was the rejection of all the theories advanced prior to the Space Age to explain the origin of the Moon. In the ensuing decade a new hypothesis was developed; not, of course, that everyone agrees with it!
In the 1990s the first of a new wave of probes used sophisticated sensors to survey the composition of the lunar surface, to chart its topography, and to map gravitational irregularities for insight into the internal structure. In this century, other nations have started to send probes, turning the scientific investigation of the Moon into a truly international venture.
One major discovery was that there is water in polar craters whose floors are in permanent shadow. When we return to the Moon, we will very likely establish a base of operations on a nearby patch of high ground where the Sun always shines to provide the power to mine the resources which will enable us to venture to destinations beyond.
posted 11-19-2015 08:17 AM
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