Just in case you haven’t noticed yet next Wednesday an astronomical “once in a lifetime” “event of the century”, a transit of Venus, will take place. This has naturally provoked a flood of media interest resulting in lots and lots of reports running the gamut from good to totally miserable with the average, from the history of science standpoint, tending to ropey at best. Under normal circumstances I might have taken one or the other of these articles to task here but as I was busy writing my own Transit of Venus article, for a local astronomy society journal, and public lecture, held last Wednesday in Nürnberg, I didn’t really feel like blogging about it as well. However the appallingly bad book extract on the subject posted yesterday on the Scientific American website made me change my mind. Just how bad is it? This post is a very serious candidate for the worst piece of history of science writing of the year. In fact any competitor is going to have to try very, very hard to beat it for this title.
The piece in question is titled The Man Who Knew Venus Would Transit the Sun and is an excerpt from a book entitled Venus in Sole Visa by Ken Shulman. Some simple advice for my readers, “Do not read this article! Do not buy this book!” It is a total waste of both your time and your money and an insult to your intelligence. As is my wont on such occasions I will reproduce passages from the offending article and then point out the errors contained there in.
The article deals with the prediction and observation by the young English astronomer Jeremiah Horrocks of the Transit of Venus in 1639, a worthy and important subject for a history of astronomy article. The author starts with a bit of biographical background:
Son of craftspeople and perhaps farmers—there were also a few watchmakers among his forbears—Horrocks had been a local wunderkind who entered Emmanuel College in Cambridge at age 14 as a sizar—a poor student whose duties, along with studies, included the preparation of meals, waiting on tables, and custodial work. In 1635, three years after his arrival, Horrocks left the university—in all probability due to lack of funds–and returned to Lancashire, where he continued to observe the heavens with a small telescope he either purchased or received as a gift from one of the landed families whose children he tutored.
There were not just watchmakers amongst his forebears; Horrocks’ own father was a watchmaker. Although his future development definitely shows that Horrocks was an extremely intelligent young man there is no historical evidence what so ever to support the claim that he was recognised as a “wunderkind” or child prodigy. If as I suspect, due to the juxtapositioning, the author is inferring this from the fact that Horrocks entered Emanuel College at the age of 14 then he is mistaken; throughout the Early Modern Period 14 was the normal age for university matriculation. Horrocks did indeed leave the university in 1635 without graduating but we don’t know why. The claim that it was probably due to poverty is a myth created in the nineteenth century. This claim is highly unlikely as Horrocks’ family were known to have been wealthy, his entering university as a sizar was probably due to puritan ethics rather than financial necessity, and such a radical change in their circumstances would probably have been documented. We know that he purchased his first telescope, for 2s. 6d., himself because he says so in his correspondence. By the time he observed the transit he had acquired his third telescope, an above average model according to his own account. All of this is, of course, just nit picking but we have only just started; it gets worse, much worse.
Having dealt with the biographical we now move on to the astronomy of the period, to Kepler, Brahe and Copernicus:
The revolutionary discovery was Kepler’s, and would be his most memorable contribution to science. One century before Kepler, Nicolas Copernicus stated that the sun—not the Earth—was the center of our planetary system. Heliocentrism helped astronomers reconcile cosmic theory with the real-life cosmos they saw before them. Yet there were still many phenomena that Copernicus’ bold shift did not explain: retrograde motion—the apparent backtracking of planets—was one; others included eclipses and planetary conjunctions that should not have occurred if the Copernican model of the solar system was accurate.
Copernicus’ De revolutionibus was published in Nürnberg in 1543. Johannes Kepler was born in 1571. I didn’t realise that centuries were so short in the Early Modern Period.
Yet there were still many phenomena that Copernicus’ bold shift did not explain: retrograde motion—the apparent backtracking of planets—was one…
History of Astronomy 101:
Question: What is the principle feature of Copernicus’ heliocentricity that increases its explanatory power as a theory of planetary motion in comparison to the geocentric theory of Ptolemaeus?
Answer: It provides a natural explanation for retrograde motion.
In case any of my readers don’t recognise the enormity of the authors mistake here and why it completely disqualifies him to write about the history of astronomy it’s as if a football writer would say that Germany won the World Cup Final against England in 1966 or a historian would write that Charles I won the English Civil War against Cromwell.
…others included eclipses and planetary conjunctions that should not have occurred if the Copernican model of the solar system was accurate.
The sentence quoted above is just mind bogglingly stupid. I’m not even sure what it’s supposed to mean. Whatever it is it is just plain and simple rubbish.
Kepler intuited that these discrepancies were due to the true shape of planetary orbits.
No he didn’t! First of all, the “discrepancies”, as quoted above, are a figment of our author’s imagination. Secondly, Kepler was initially only concerned with the accurate size and duration of the planetary orbits; he only stumbled across his shape changing innovations during his analysis of the orbit of Mars.
After a prolonged and trying period analyzing Brahe’s data (Kepler gained access to Brahe’s figures while working as Tycho’s assistant in Prague in the 1590’s,) Kepler concluded that Mars traveled around the sun in an ellipse and not in a circle.
Tycho and Kepler first met in 1600. They didn’t start working together until 1601; a partnership that was very short, as Tycho died in the same year.
Horrocks cottage observatory in Much Hoole was a far cry from Tycho Brahe’s palatial skylabs in Denmark and Bohemia
It is not actually known from where in Much Hoole Horrocks observed the 1639 Transit. However the house that is traditionally assumed to have been his “observatory” is a three-story country mansion and not a cottage.
But Horrocks was not delusional. In 1610, Galileo had used a telescope of just 10x magnifying power to confirm that Venus was a planet and not a star; the finding cast the nature of the entire universe into doubt. In 1631 Pierrre (sic) Gassendi had successfully observed a transit of Mercury with a makeshift camera obscura he’d mounted in a spartan (sic) Paris garret.
Galileo was using 20x and 30x telescopes in 1610 to observe the heavens and we can assume, given his comments about the superiority of his instrument, that Horrocks was probably using a 30x telescope for his transit observations. Gassendi used a telescope to project the image of the sun onto a scaled sheet of paper to observe the 1632 Transit of Mercury and not a camera obscura; the same technique employed by Horrocks for his transit observations.
…to confirm that Venus was a planet and not a star; the finding cast the nature of the entire universe into doubt.
Words fail me! In seventeenth century astronomical terminology all heavenly bodies are stars but the seven planets, Moon, Mercury, Venus, Sun, Mars, Jupiter and Saturn, were planets and had been since the Greeks coined the word. What Galileo, as well as Marius, Harriot and Lembo all independently, discovered telescopically was that Venus has phases like the Moon; phases of a type that proved that Venus orbits the Sun and not the Earth. Again this is an error is on a level that completely disqualifies the author from writing on the subject.
It wasn’t that the German’s math was flawed, Horrocks saw. It was that Kepler had misunderstood the nature of the force that causes the planets to travel around the sun in ellipses. Kepler believed the sun first pulled the planets toward it, and then, when they were close, repelled them. This alternating push and pull, according to Kepler, was the force that generated the elliptical orbits. Horrocks believed this was wrong, and that the error had skewed Kepler’s calculations.
The Englishman was a very unlikely challenger for such a heavyweight. Kepler had studied with the finest professionals of his day, had enjoyed royal patronage, and had access not only to Tycho’s magnificent data set but to his equally magnificent facilities. In contrast, Horrocks was a poor university dropout working in a remote provincial town that most likely did not even have a library, let alone an observatory. His mind, of course, was keen. But it was also a mind that worked in almost total isolation, and in a country that had never attributed great importance to the study of the stars.
Kepler, in fact, only had one teacher, Michael Maestlin, who was however one of the leading European astronomers of the age. He did have Tycho’s data but so did Horrocks in the form of the Rudolphine Tables. Kepler didn’t have access to Tycho’s facilities as these belonged to Tycho’s heirs who sold them off after his death. He didn’t however need them, as he was a theoretical astronomer and not an observational one. Kepler’s royal patronage was a curse rather than a blessing as his employers seldom paid him his retainer and he spent almost all of his life fighting debt and poverty. We don’t know which books Horrocks actually owned but it is very clear from his papers that he knew and had studied all of the leading astronomical literature of the period. Very few working astronomers in the first half of the seventeenth century had or used observatories. Their few instruments were all highly portable and they just carried them to wherever they wished to observe, set them up and observed. Horrocks’ observation conditions were no different to those of Galileo, Thomas Harriot, Simon Marius or many others who wrote astronomical history in this period and to claim otherwise is misleading pathos. Far from being isolated Horrocks was a close friend of John Wallis one of the leading mathematical scholars of the age. He also corresponded extensively with the Gresham Professor of Astronomy Henry Gellibrand and his successor Samuel Foster both of whom were integral members of the English mathematical community of the time.
Still, Horrocks continued to trust his own eyes and his intuition. He constructed a pendulum and studied its Earthward and upward swings; from this simple experiment he concluded that a planet, left to its own devices, would always travel in a straight line. And that the sun, conversely, would attempt to cause the planet to revolve around it in a circle. (Horrocks’ description of the dynamic between sun and planet is very close to the force that his compatriot Isaac Newton would identify as gravity some four decades later.) It was the ongoing dialogue between these two forces, Horrocks concluded, that dictated the elliptical orbits, not the push me–pull you sun of Kepler’s cosmos. More importantly, it was this difference in dynamic that accounted for the inaccuracies he’d found in the Rudolphine Tables.
The distinction between the theories—and the distortions that distinction might produce—was minor, Horrocks knew. But scaled against the solar system, at distances that could be cadenced in thousands of Earth radii, it was just large enough to turn a non-event into a full-blown transit of Venus. Kepler’s Rudolphine Tables had Venus passing just above the sun on November 24, 1639. Horrocks predicted that Venus would pass in front of the sun, just as it had eight years earlier.
Horrocks did indeed develop an alternative theoretical model to Kepler’s to explain the planetary orbits but he did not use a pendulum to do so. (His theory is however much, much further removed from Newton’s theory of gravitation than the author suggests) In order to explain his model he made a verbal analogy to the movement of a pendulum. These differing models have absolutely nothing to do with the numerical errors in the Rudolphine Tables or Horrocks’ corrections of them. Horrocks discovered the errors through empirical observations, he was using a telescope Tycho’s observations the basis for the tables were naked eye observations, and he made the necessary corrections based on those observations.
This book extract presented by a university student as an essay in a history of astronomy 101 course would earn a big fat F and the suggestion that the student should perhaps choose another minor. If the course were his major then he would have really big problems. Published on the website of one of the worlds leading popular science journals it is nothing short of a scandal and an insult to every serious historian of science working in the world today.