Review of Parallax: The Race to Measure the Cosmos

Review of Parallax: The Race to Measure the Cosmos

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Metanexus:Views 2002.01.18 2132 words

Parallax can be fun. Like when you are sitting in the bathtub and makingyour fingers get longer or shorter depending on the angle at which you placethem in the water. Or when you observe the amazement of a child with a strawin a glass of water. The straw may go in at one angle, but when you lookthrough the glass…the straw has moved or, horror of horrors!, beenbroken.

Parallax, however, can also be a problem. And, as Karl Giberson observes ishis review of Parallax: The Race to Measure the Cosmos by Alan W. Hirshfeld(New York, NY: W. H. Freeman and Company Publishers, 2001, 314 pages, $23.95hardcover)

The problem has to do with the appearance of the heavens when viewed froman earth in motion. If the earth does indeed travel around the sun then itshould be continually finding itself roughly 186 million miles away fromwhere was six months previously. If this is indeed what was happening thenit would follow that the stars overhead would move back and forth a bit,since earth-bound observers were viewing them from different locations. Ifthe stars overhead were not moving back and forth, then perhaps the earthwas not going around the sun.

What to do? That is always the question when dealing with perspective–whichis, of course, the essential element in parallax. And it is not merely theproblem of the point of perspective (the limits of location), it is also theproblem of the medium of perspective (as with the air and water problem).Basically, it is one of the most fundamental challenges of science: how tofind out what’s really going on when you are really limited to your owntime and space. Of course, others would say that this is not a challenge tobe overcome but a limitation to be expected and accepted. Read on, and enterthis interesting debate.

Today’s columnist, Karl Giberson, is Canandian, He is the editor of ResearchNews & Opportunities in Science and Theology and a long time participant inthe science and religion dialog. He is also part time professor of physicsand history of science at Eastern Nazarene College. With a Ph.D is Physics,he has, over the years, become more interested in the creation evolutioncontroversy, having published one book Worlds Apart. There is another bookin the pipeline as well, titled Species of Origins: America’s Search for aCreation Story. He has also published articles on the anthropic principle,divine action, and a number of popular pieces in Books and Culture.

–Stacey E. Ake


Subject: A Review of Parallax: The Race to Measure the CosmosFrom: Karl GibersonEmail: <>

Astronomer Alan Hirshfeld’s Parallax: the Race to Measure the Cosmos is arecent addition to the many fine volumes that have been appearing in thehistory of science, a field that is coming into its own after decades ofhiding within and lurking around the fringes of traditional sciencedepartments. For a great many years, the histories of their disciplineswere written by scientists themselves, like Hirshfeld, but who, unlikeHirshfeld, portrayed scientific advance as somehow inevitable and scientistsas men of great genius and few dimensions. Discussion of the personal livesof scientists tended to focus on eccentric tidbits good for entertainingstudents when they were learning arcane theory. The great concentration ofNewton, who would forget to eat while working on a problem, the absentminded Einstein who would come home to wrong house, the irreverent wit ofFeynman who tormented the military at Los Alamos by breaking into top secretsafes and leaving notes–such delightful, if decontextualized, trivia hassometimes been about as much history as one could find in science. Lessbenignly, when scientists would treat historical episodes like the GalileoAffair, or Wilberforce’s great confrontation with Huxley over evolution,the accounts would inevitably portray the scientific player as the hero,little David heroically doing battle with whatever Goliath — oftenreligion, sometimes Aristotle — was standing in their way.

History of science, in some sense, began in earnest, albeit on a smallscale, at Harvard University, when George Sarton arrived as a refugee fromBelgium during World War I. For most of the century just past there reallywas no discipline of the history of science and few departments. Thelegacy of that long professional struggle can be seen in the particularindividuals who are now recognized as its veterans– Owen Gingerich atHarvard, a leading authority on Copernicus and Kepler, who teaches but hasnever taken history of science. Or Abraham Pais, who has writtenbiographies of Einstein and Bohr, and a definitive history of particlephysics, yet whose training and professional affiliation was conventionalphysics.

Times have changed. There are now professional historians of science likeDavid Lindberg, Ronald Numbers, and John Hedley Brooke, who have helped tooverturn the simplistic pictures of the past. And they have students.Today, in fact, there are more students at Harvard pursuing history ofscience than conventional history. There are journals in which they canpublish and conferences for them to attend. And, of no mean significance,there are jobs for them after they graduate.

One happy result of this maturation of the history of science has been thesteadily improving quality of books that present episodes in the history ofscience with remarkable insights that capture the genuine excitement of thescientific quest embedded firmly in the social and historical circumstancesof its time. No longer are scientists treated as eccentric abstractionsonly tentatively embedded in time and space; they come to life, with allthat is implied by that most challenging metaphor. And the excitement thathas been discovered in the history of science has drawn and continues todraw highly literate writers, historians, and scientists into its unexploredlabyrinths.

All this has been to the benefit of the reading public. Dava Sobel’s bookLongitude, for example, became an international best-seller, was translatedinto more than twenty foreign languages, and was adapted for television byboth PBS and A & E. (Someday, hopefully, Hollywood will get over its fearof science and put Galileo and Darwin on the big screen.)

Parallax: The Race to Measure the Cosmos is a recent excellent volume in thehistory of science, masterfully written by University of Massachusettsastronomer Alan Hirshfeld, who has won a national award for his sciencewriting.

Like its predecessor Longitude, to which it is compared by an endorsement onthe front of the dust jacket, Parallax unravels a small thread from thehistory of science and examines it in detail–sufficient detail to avoidcaricature and oversimplification. The term parallax refers to the apparentchange in the position of an object when viewed from different locations.The standard example is your finger, held in front of your face, whichappears to jump back and forth when viewed alternately by your left andright eyes. This simple phenomena is at the heart of a critical problemthat plagued astronomers for centuries.

The problem has to do with the appearance of the heavens when viewed from anearth in motion. If the earth does indeed travel around the sun then itshould be continually finding itself roughly 186 million miles away fromwhere was six months previously. If this is indeed what was happening thenit would follow that the stars overhead would move back and forth a bit,since earth-bound observers were viewing them from different locations. Ifthe stars overhead were not moving back and forth, then perhaps the earthwas not going around the sun.

The attempt to detect parallax-induced motion in the heavens is a topic thathas generally lurked in the background of the history of science, largelybecause it is the story of continual failure. And, when the parallax of thestars was finally measured in the nineteenth century it wasanti-climactic–the motion of the earth around the sun, which had finallybeen empirically established, had long since been established on other,indirect, grounds. Nobody needed observational proof any longer and theman who finally accomplished the heroic task of measuring Parallax, anextraordinary genius named Bessel, never became particularly well known.

Hirshfeld brings the long frustrating search for parallax to life inParallax: The Race to Measure the Cosmos. The measurement is themeasurement of the actual distance to a star–any star outside our solarsystem. The story begins in earnest with the naked-eye observations ofTycho Brahe who advanced astronomy without a telescope as far as was humanlypossible. But Brahe never detected any parallax motion of the stars,although he did discover a number of even more significant things, like theactual locations of comets. Subsequent telescopic studies by Newton’snemesis Robert Hooke were equally unsuccessful. James Bradley, and WilliamHerschel who, like Hooke, employed observational techniques suggested byGalileo, also failed. Efforts to measure stellar parallax gained momentumin the early 19th century with remarkable improvements in telescopetechnology by German craftsmen such as Joseph Fraunhofer, who set newstandards for engineering excellence in the design and production oftelescopes.

After frustrating many generations of diligent observers, stellar parallaxwas, paradoxically, observed by three contemporary astronomers almostsimultaneously in the late 1830s. Thomas Henderson measured the parallaxof Alpha Centauri, Wilhelm Struve measured Vega, and Friedrich Besseldetected apparent motion of 61 Cygni. Prior claims to have measuredparallax had been shown to be mistaken so these new claims were subjected toan intense and skeptical scrutiny. By consensus of the astronomicalcommunity, Bessel got the credit for the first successful measurement of thedistance to a star.

Bessel’s observational prowess, which had a strong theoretical dimension,was legendary. He developed the concept of the twice-built telescope.Bessel knew that any telescope, even the extraordinary instruments comingout of Fraunhofer’s shop, had flaws that would interfere with the kind ofprecision measurements necessary to detect parallax. So he figured out away to build a mental model of the telescope that would expose its variousidiosyncrasies. Knowledge of the mental model allowed the user to makeallowances for the limitations of the telescope. Bessel would, for example,measure things that were known with great precision, record the telescope’sconfiguration, and make a mental adjustment for the tiny, but known, errorsthus observed.

Bessel’s twice built telescope gets the credit for the first parallaxmeasurement. It was truly a major achievement capstoning more than twocenturies of careful work on both the design and application of telescopes.Paradoxically, however, Bessel’s achievement created only a minor splash inthe history of science and therein lies a critical insight into the natureof scientific advance. The traditional wisdom is that scientific advance isdriven by observation or, as is often the case, lack of observation. Forseveral centuries the lack of evidence for parallax was used to argue thatthere was no parallax–the earth was not moving. In much the same way, manytoday would argue that the lack of a signal from extraterrestrials meansthat there are none. However, in both cases the absence of a signal or ameasurement is inconclusive. Explaining away the failed measurement isnot difficult and can readily be done if there are good reasons to do so.In the case of parallax, the glorious success of the Newtonian model of theuniverse, with its untethered earth racing around the sun at thousands ofmiles per hour, was so compelling on non-observational grounds, that it wasalmost universally accepted. When Bessel actually measured the motion ofthe earth he was simply confirming what everybody already knew. It was anon-event in many ways.

Parallax: The Race to Measure the Cosmos is an outstanding book; it differsfrom Longitude in having more science and a longer historical sweep; italso has less politics and human drama. The race to measure longitude wasenlivened by the fact that sailors were everywhere dying because of failedlongitude measurements and there was a gigantic cash prize motivating theplayers. No such human tragedy undergirded the search for parallax.

Nevertheless Parallax is not without its dramatic elements. Hirshfeldsuccessfully maintains a biographical focus that highlights the humandimensions of the race to measure the cosmos. Many chapters also begin withpersonal anecdotes as the author shares his own scientific history with thereader. The result is a comforting sense that the author is a part of thetradition that he so ably portrays in the book.

Parallax is an excellent volume in the new history of science. Hopefullyit will enjoy the same sort of success as Longitude and provide yet anotherbridge between science and the humanities.

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