The ultimate judge in science is always what nature itself reveals based on observations, experiments, models, and testing. Science is not merely a body of knowledge, but a method by which we attempt to understand nature and how it behaves. This method begins with…
Astronomy is defined as the study of the objects that lie beyond our planet Earth and the processes by which these objects interact with one another. We will see, though, that it is much more. It is also humanity’s attempt to…
Although Herschel’s discovery of Uranus made his reputation, it was far from being his most important contribution. During the 18th century, astronomers had measured the proper motions of a reasonably large number of stars. (Proper motion is the slow drift of a star with respect…
The foremost observational astronomer of the period was William Herschel. Herschel was born in Hanover, Germany, in 1738, but he moved to England as a young man to avoid the Continental wars. He settled in Bath and made a living as a musician…
Since every planet is attracted not only by the Sun but also (much more weakly) by all the other planets, its orbit cannot really be the simple ellipse described by Kepler. Newton was therefore willing to entertain the idea that God might occasionally need to readjust the…
In the first part of the 18th century, the inverse-square law was subjected to several dramatic tests. The first concerned Earth’s shape. Newton had argued that Earth’s rapid rotation on its axis must cause Earth to depart from perfect sphericity. Instead,…
Kepler’s laws received a physical explanation only with the publication of English physicist and mathematician Isaac Newton’s Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy, 1687). Here Newton announced his laws of motion, as well as the law of universal gravitation: any two particles…
German astronomer Johannes Kepler embraced Copernicanism wholeheartedly. Nevertheless, he may be considered the last astronomer, and one of the greatest astronomers, in the old tradition—one of the last for whom the Almagest was still a part of the research literature. Kepler had begun with…
In 1609 Italian scientist Galileo Galilei, using his own telescope, modeled on an invention recently made in the Netherlands, discovered that the Moon, far from being smooth and utterly unlike Earth, had mountains and craters. By using the lengths of their shadows, Galileo…
Danish astronomer Tycho Brahe was a good example of those who admired Copernicus’s achievement in tying all the motions of the planets more closely to the Sun but who were unable to accept the motion of Earth. Brahe worked out an alternative cosmology, known…