Spring sky, the Bard and Bacon
This week, we mark the Ides of March: the halfway point of our trek through this month. The most famous reference to this date is, of course, the assassination of Julius Caesar on March 15, 44 B.C. at the hands of Roman patriots attempting to prevent the ambitious Caesar from transforming the Roman Republic into a dictatorship. William Shakespeare gave us many of our enduring modern images of this event when he dramatized it in his play, Julius Caesar, written more than 1,600 years after the events occurred. Shakespeare added many elements to enliven the story, including astronomical references. Early in the play, a soothsayer warns Caesar “beware the Ides of March” referencing the Roman calendar which was based upon the best astronomical observations of the time.
Caesar’s wife, Calpurnia, also warns him on the night before his assassination that she has seen omens in the sky that foretell his death. Like most Romans of his time, Caesar accepts the superstition of astrology but does not believe the portents seen apply to him personally. Calpurnia responds, “When beggars die, there are no comets seen; The heavens themselves blaze forth the death of princes.”
Comets were an astronomical mystery in Shakespeare’s time as well as in Caesar’s. They seemed to appear randomly and without warning; a bunch of celestial outlaws who cared nothing for the law and order of the heavens. Today, we know that comets are essentially dirty snowballs in orbits that mostly keep them far from the sun where they are invisible to us. When they venture into the inner solar system and their surfaces are warmed by the sun, their outer layers of ice evaporate, spewing forth gas and dust to form their prominent tails. Most of the comets we see move in orbits that only bring them into view once every few hundred or few thousand years. On the scale of human lifetimes, they seem to suddenly appear at random. The famous Halley’s Comet has a shorter period than most, returning every 76 years. But throughout human history, no one recognized it as the same object until Edmund Halley applied the newly-discovered physics of his friend Isaac Newton to calculate the orbit of the comet in 1705 and predict its return in 1758. He did not live to see it but when the comet returned as he had predicted, it became known as “Halley’s Comet.” Before Newton and Halley however, comets seemed to be dangerously unpredictable interlopers trying to inject chaos in the clockwork order of the heavens. It’s not surprising that they came to be seen as omens of disaster which might strike without warning. Even our English word, “disaster, ” comes from the Greek words for “bad star.” It is this sense of disaster that Calpurnia associates with the comet she has seen and she concludes that disaster must apply to Caesar since she believes something as important as the heavens would never be concerned with the poor or common people.
“Julius Caesar” is not the only one of Shakespeare’s plays that references astronomy. In the last act of “The Merchant of Venice,” Lorenzo says to Jessica, Sit, Jessica. Look how the floor of heaven Is thick inlaid with patens of bright gold.
There’s not the smallest orb which thou behold’st But in his motion like an angel sings, Still quiring to the young-eyed cherubins; Such harmony is in immortal souls, But whilst this muddy vesture of decay Doth grossly close it in, we cannot hear it.
Here Lorenzo is referring to the mathematical models of the sky formulated by the great astronomer Ptolemy, born about 150 years after the time of Julius Caesar, and still widely accepted in Shakespeare’s own time. Ptolemy imagined the Earth at the center of the universe, as had those before him, but he devised ingenious combinations of circular motion to explain the observed motions of the sun, moon, planets, and stars.
Explaining the motion of the stars was pretty easy; one could assume they were attached to a giant sphere around the Earth which turned once per day to account for the rising and setting of all the stars. Since the sun and moon don’t move at the same rate as the stars, he had to assume they were each attached to a separate sphere which turned at a slightly different rate. The real problem was the five planets visible to the naked eye: Mercury, Venus, Mars, Jupiter, and Saturn. Their motion was much more complicated. As shown in the diagram, to account for observed planetary motions, Ptolemy had to assign each planet to its own sphere with a complicated epicycle sub-mechanism to produce the observed motion.
The Greeks assumed the relative sizes of these spheres were small ratios of whole numbers, so just as the length of the strings on a harp are related by simple ratios to give harmonious sounds, so they assumed the motion of spheres with sizes related by simple ratios would produce harmonious sounds of a kind that could not be heard by human ears – the “Music of the Spheres.”
This “Music of the Spheres” is what Lorenzo refers to in the above quotation from “The Merchant of Venice.” But notice Shakespeare has made a mistake; Lorenzo speaks as if each star had its own sphere, rather than one sphere for all the stars and a separate sphere for each planet, as the Greeks envisioned. Therein lies a clue to discrediting a fringe belief about the authorship of Shakespeare’s plays.
Shakespeare was born to a poor family in the small town of Stratford-upon-Avon and although little is known of his education, there appears to be no evidence that he had much formal education. Beginning in the 19th century, some questioned whether someone of Shakespeare’s humble origins could have written such masterful plays. They suggested the plays had been secretly written by wealthier and better educated contemporaries, such as the great philosopher Francis Bacon. Bacon was thoroughly educated in classical Greek astronomy and would never have made the sort of error we see in Lorenzo’s speech. But as Isaac Asimov once pointed out, it is exactly the kind of mistake one might expect of a largely self-educated man of the time like Shakespeare.
Our night sky is full of wonder and beauty that have engaged the imaginations of people for millennia. Take advantage of this endless natural resource by visiting the Adirondack Public Observatory. The volunteer staff of amateur astronomers will be happy to assist you and answer questions. The observatory is open to the public on the first and third Fridays of each month, weather permitting of course. For updates and notices, check out our website at apobservatory.org and our Facebook page. On our public observing days you can also call the RORO (Roll Off Roof Observatory) at 518-359-6317 to talk with one of our astronomers. Observing starts about one half hour past sunset. Clear skies!