The Great Astronomers, R.S. Ball
Reviewed by Jim Roe
This book, written in 1895, is available from Project Gutenberg at http://www.gutenberg.org/ebooks/2298 in formats suitable for the Kindle and Nook. I found it an easy read (I enjoy the prose styles of Victorian England). It does not give really extensive details of the lives and work of the astronomers selected but I found interesting facts about each that I had not known previously or had underestimated. I will give some of these below.
Lived and worked on Rhodes ca. 160 BC. Deemed the "Father of Astronomy," discovered the precession of the equinoxes. I'm not sure how he did this.
Much maligned by modern know-it-alls, yet this man made such reasonable, convincing arguments for his explanations of the movements of Solar system bodies that they stood for some 1,400 years, much longer than anyone else to date. Galileo had a hard job to convince his contemporaries that the Copernican system was superior to Ptolemy's simply because Ptolemy's system served for the purposes for which it was intended. Ptolemy was guided by the "obvious" principle that Nature must adhere to "perfect" circles and I am struck by how modern scientists also believe in such "perfect" scenarios, as in, especially, modern particle physicists' enamor with "symmetry" and "super-symmetry."
Also, I have often wondered whether Ptolemy's epicyclical scheme could be expressed as terms in a Fourier series that would show he was on the right track, even if such mathematics had not been invented in his day? (Fourier analysis is a method to break down periodic functions into a series of sine and/or cosine functions. Sine and cosine functions can be interpreted as circular motion. Mathematicians have proven that any reasonable function can be so expressed.)
It was, of course, Copernicus who put us on the correct path of recognizing that the Sun was the center of our local system but it could have been a lucky guess. The BIG problem at the time, for both Ptolemy and Copernicus, was the question of which moved, the Earth or the starry heavens. While both recognized that the Earth was tiny on a scale that reached to the stars it was ultimately too much for Ptolemy to negate his (and everyone else's) senses that the Earth could possibly move. Copernicus had the opposite "feeling" in that he couldn't believe that the heavens, whatever they were, or consisted of, could move. Neither knew what the stars were so maybe Copernicus was just lucky?
Tycho Brahe was the first to apply rigorous standards to observations of the sky, in particular the motions of the known planets. He discovered the supernova of 1572 and his careful measurements showed beyond a reasonable doubt that the star was immensely farther away than the diameter of the Earth. At that time the 'new' star could just have easily been believed to be an atmospheric phenomenon, as were comets. His carefully taken and preserved observations were a marvel for the time and served as the basis for Kepler's subsequent work.
What's not to know about Galileo? Ball's explanations brought about a new insight for me, however. In lectures and classes I teach I have often remarked that Galileo's discovery that the unresolved Milky Way (to the unaided eye) was really myriads of faint stars was very important. I've also told folks that the most important characteristic of a telescope is its light gathering power. The bigger the telescope objective, the fainter the objects that can be observed and that implies farther away objects and that implies more objects. I sort of skip over the "farther away" aspect because everyone knows that bright objects observed from a distance appear fainter. But at the time of Galileo nobody knew what stars are and the distances of the Universe were totally unrecognized. Yet, the observation of more faint stars than had been known previously at least gave a hint that the distance to different stars could be different.
Johann Kepler was the first data miner! He was given access to the records of Tycho Brahe and, through industrious effort and a lack of modern mathematical tools, was able to come up with reasonable explanations for the data - Kepler's three laws of planetary motion. Essentially, this was "curve fitting" and I have often wondered how well his curves fit the data, ie, I have never seen an error analysis. Isaac Newton subsequently developed the theory that showed Kepler's laws arose from the theory of gravitation. The new fact I learned from this book was that Kepler was the first to predict transits of Venus and Mercury across the face of the Sun. He was also the first to observe a transit of Mercury.
What is to say about Newton? However, I can't help but wonder if Newton had any inkling of just how famous he would become and how high he would rank among all-time thinkers and doers.
First Astronomer Royal, founder of Greenwich Observatory. Created best catalog of stars since Tycho.
First to recognize that comets are (or can be) periodic. Predicted the return of what became to be known as "Halley's Comet" that occurred after his death. More importantly was chiefly instrumental in getting Newton's Principia published.,
Discovered the "aberration of light" which is a correction to the positions of observed stars that takes into account the fact that the telescope moves from the time a photon enters the objective until it strikes the "detector" which, in Bradley's day, was the cross hair in the eyepiece. The motion of the telescope is, of course, due to the Earth's motion in its orbit around the Sun. It only became noticeable when telescopes had reached a sufficient precision.
The first to put in lots and lots of "eyepiece time" watching the heavens move through his fov. Have his sister Caroline was a huge help. Along the way, he discovered Uranus.
Brilliant mathematician, great expositor of Newton's theories. But I had forgotten that he first proposed the Nebular Theory for the formation of the Solar System
A chip off the block of his father. Extended sky surveys to the Southern hemisphere. But his work on double stars set a new standard. How to find the distance to the stars was a BIG problem. It was long recognized that double stars could easily arise from chance alignments of two stars one of which is much farther away than the other. The idea of parallax was also known but how does one measure it. In those days, the location of the fixed stars was not known precisely enough to compare measurements taken at different times. But with double stars one gets a built in reference so it seemed worthwhile to monitor the separations of known double stars at different times during the Earth's revolution around the Sun. John Herschel set out to do this in a systematic manner. What he discovered was that not only could the separation vary with time (but not correlated with the Earth's motion) but the position angle as well. Some of the stars were clearly orbiting each other - what we now call binaries. These give the best estimates of distances of any other technique.
Earl of Rosse
More of an optician (called "mechanic" in those days) than astronomer, but used his six foot (diameter) reflector to observe that many nebulae exhibited spiral arms. Because the scientific method requires an independent confirmation and no one else had big enough telescope the claim went unsupported until photography techniques confirmed it much later.
Airy is most familiar today from his descriptions of the "Airy disk" which demonstrates the limits to the resolving power of telescopes - but no mention is made in this account? On the other hand, Airy (among his other works) was the first to examine the phenomenon of astigmatism and came up with a fix still used today.
Not an observational astronomer but a "mathematical researcher" maybe in the manner of Kepler. Le Verrier studied the deviations in the observed motions of Uranus to decide that there must be another planet out there. His calculations showed such a planet should be at such and such and asked Galle at the Berlin observatory to look for it. Galle found it on the first night of searching but it took another few days to verify that the "new" star not present on his charts was not a nova or a long period variable star that had been at minimum when the chart was made. He did this by observing its motion relative to the fixed stars. It was, of course, the first time Neptune was observed. I saw the telescope with which this discovery was made when I visited the Deutsche Museum in Munich in 2008.
It is interesting that, after this great success, Le Verrier turned his attention to Mercury whose motions could not be accounted for by the then known planets. A search for another planet was undertaken but nothing was observed. It was still a mystery at the time of the writing of this book. Not until Einstein appeared to have solved the problem with his Theory of General Relativity did the matter come to rest.
According to the author (Ball) Adams was second only to Newton (at least among Englishmen) in his theoretical prowess. But for most us (me at least) the state of celestial mechanics had entered the diminishing returns stage. Ie, the explanations of very small matters that, nevertheless, reinforce the validity of Newton's theories was good stuff. A matter I was not familiar with though was very interesting to me. In particular it had been noted that using modern values for the period of the Moon, projecting backward a couple thousand years to recorded eclipses of the Moon revealed an error of some one degree. Laplace had accounted for this by taking into account perturbations of the Moon's orbit by the Sun but Adams showed Laplace's result only accounted for about one half the observed data. The remaining half of the error remained a mystery until it was suggested that the difference was due to the Earth's rotational period had slowed down. Ie, the period of the Moon's orbit was measured in "days" which are defined by the Earth's rotation. This illustrates one of my favorite peeves - scientists must (should) be very careful of their assumptions.
Another fascinating feature of this investigation. While the Earth's orbit is nominally an ellipse, perturbations of this ellipse due to the gravitational influences of all the other planets (and even asteroids) are a fact of life. In practice, these days, the positions of the planets and derived by integrating all these effects in super computers (at JPL, I believe). One of the results of all these calculations is that, while the "ellipse" of the Earth's orbit is constantly changing, the semi-major axis never changes. This means the eccentricity and tilt of the orbital plane are the only things that change. These changes are very slow, to be sure, but it appears that the Earth's orbit has been becoming closer to a circle for the past many millennia.