Sunday, December 16, 2007

Emerson’s Science-Baffling Star

The magnetism which all original action exerts is explained when we inquire the reason of self-trust. Who is the Trustee? What is the aboriginal Self, on which a universal reliance may be grounded? What is the nature and power of that science-baffling star, without parallax, without calculable elements, which shoots a ray of beauty even into trivial and impure actions, if the least mark of independence appear? The inquiry leads us to that source, at once the essence of genius, of virtue, and of life, which we call Spontaneity or Instinct. We denote this primary wisdom as Intuition, whilst all later teachings are tuitions. In that deep force, the last fact behind which analysis cannot go, all tings find their common origin. For the sense of being which in calm hours rises, we now not how, in the soul, is not diverse from things, from space, from light, from time, from man, but one with them and proceeds obviously from the same source whence their life and being also proceed.

Emerson’s use of this lovely metaphor, his “science-baffling star,” to portray the divine element which he believes all people possess and which can manifest itself if only we will trust our inner nature, occurs in his essay “Self-Reliance,” which was published in a collection titled Essays: First Series in 1841. The essays are based on lectures given by Emerson during the preceding years.

Although one can enjoy and appreciate this passage purely in its own context, it is fun to know the star Emerson most likely had in mind can be observed on summer and fall evenings from northern latitudes.

Friedrich Wilhelm Bessell, a German astronomer, announced in 1838 that he had succeeded in measuring the stellar parallax of 61 Cygni using an extremely precise Fraunhofer 16-centimeter heliometer. Bessell was able to determine the distance, 11.4 light years, through mathematical computations on his parallax determination of 2/3s of an arc-second. 61 Cygni thus became the first star whose distance was accurately measured, a task that baffled scientists for centuries.

Parallax can be understood quite simply by holding one’s finger at arm’s length and sighting along it at the background while keeping one eye closed. After the initial sighting, open your second eye and close the first. Your finger will appear to have moved in relation to the background. This occurs because the distance between your eyes forms a triangle with its apex at your finger tip. Using math, the length of your arm can be determined by knowing the precise distance between your eyes (the triangle’s baseline) and measuring the apparent shift of your finger against the background, which establishes the angle of the triangle’s apex (your finger’s parallax). Of course, one’s arm can easily and more simply be measured by other means. The distance to a star cannot.

In the wake of Copernicus and Kepler, astronomers realized they could establish an enormous baseline, the width of the Earth’s orbit, by taking measurements six months appart of a star in relation to background stars. In fact, early arguments in favor of a geocentric solar system (i.e. the Earth being the center of the universe), included the point that stellar parallax had not been detected. If the Earth truly moved, it should be found. What the geocentric proponents did not count on was the vast distance of the stars, which makes the apparent shift of even the closest stars quite tiny indeed.

By Bessell’s day the heliocentric solar system had long since been established and the orbital elements of the planets had actually been worked out so the size of the Earth’s orbit was known. Still, one had to choose an appropriate star to measure. This was done using another form of stellar motion known as “proper” motion. Some stars, being closer to our own solar system than others, are seen to move over time in relation to more distant stars. That is, the motion would not be cyclic during the course of one year (resulting from Earth’s motion) but would actually be due to the motion of the star itself. The stars with the highest proper motion could be assumed to be the closest to us and the most likely to exhibit stellar parallax. 61 Cygni had the highest proper motion of any star known at that time — 5 arc-seconds annually — and was therefore of considerable interest to astronomers.

Successfully measuring its parallax, the equivallent of measuring the size of a small coin at several miles, was a major feat of technical innovation and design.

61 Cygni, can be found in the constellation Cygnus the Swan, whose primary asterism is commonly described as the “Northern Cross.” It is actually a double star consisting of two k spectrum red dwarfs which can be separated with a good pair of binoculars or a small telescope. They present a beautiful chrome orange color in telescopes, and are of interest not only because of their historical significance but because they are the coolest and least luminous dwarf stars visible to the naked eye (from a dark sky site). They can be readily observed with a small telescope from urban areas despite light pollution.

For more on 61 Cygni, see James B. Kaler’s The Hundred Greatest Stars. 61 Cygni is entry 87. Alan W. Hirshfeld’s book, Parallax: The Race to Measure the Cosmos, tells the tale of the quest to find the distance of the stars.

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