History behind discovery of supernovas


By Tom Burns - Stargazing



Jupiter, Mars, and Saturn are slowly working their way from the morning to the evening sky. Their presence reminds me of the strange case of Tycho Brahe.

Tycho loved wine, women, song, and astronomy, not necessarily in that order. In fact, Tycho lost his nose in a sword fight over a woman or the interpretation of a mathematical equation (the historical sources are in dispute) during his misspent youth.

Undaunted, Tycho had a slew of false noses made. They came in various colors and materials, including a golden honker that flashed in the sun. Tycho figured that even a nasally impaired person should look good in his noselessness.

His relatives expected him to become a lawyer or a chemist, you know, something useful. In 1572 you did what your relatives told you.

November 11 of that year was a night like any other. As Tycho walked wearily from his chemical lab, mentally cursing the profession his parents had chosen for him, he followed his nose to the constellation Cassiopeia. And there it was — a star where no star had been before.

It was a rare and astounding event. Since the ancient Greeks, the sky had been perceived as unchanging and absolute. A new star was a startling reminder of the new science that was sweeping Europe. Everything, even the immutable sky, was subject to change.

He carefully noted the star’s position and the changes in its brightness. For the next two weeks, it was the brightest star in the sky, outshining even mighty Venus, and was visible in full daylight.

Tycho realized his data was important to scientists who were trying to understand how stars work.

But what was he to do? It was not considered proper for a noble of his station to publish a book, and a printed record of his observations would signal a final break with his relatives’ wishes.

Well, in 1573 he did publish. His book was an interesting blend of the new science and the old superstitions. On one hand, he included exact positional data and a careful record of the star’s changing appearance.

Yet much of the work detailed the astrological significance of the event. Since the star was at first as white and brilliant as Venus, the goddess of love and beauty, he said it would produce a period of peace. But since the star had faded to the blood-red color of Mars, the god of war, an era of “wars, sedition, captivity, death of princes, pestilence, and venomous snakes” would follow.

We now know that Tycho’s star was a supernova, the cataclysmic explosion of a star in our own galaxy. Only one other supernova in our galaxy has been recorded since then. Thus, Tycho’s 400-year-old data is crucial to our understanding of how and why some stars end in such a spectacular way.

You can find its approximate location by looking low in the northeastern sky after midnight for the “W”-shaped constellation Cassiopeia. Look just above the star Kappa for the approximate position of the supernova.

Unfortunately, you won’t see anything, even in a large telescope.

In 1952, astronomers used radio telescopes to scan the position. They looked long and hard for a sign of the star that exploded. All they found was its ghost, a faint shell of gas and dust over 120 trillion miles in diameter.

That “supernova remnant,” as it is called, is expanding at a rate of 600 miles per second and is about 10,000 light-years away. (One light-year translates to about 6 trillion miles.) The light from this cosmic explosion took 10,000 years to get to Tycho’s eyes in 1572. He was observing an explosion that happened 1,000 centuries before he looked up.

It was an explosion of unbelievable proportions. Modern astronomers have calculated that it burned briefly with the brilliance of 300 million suns.

Tycho’s book sealed his fate. The king of Denmark set him up in his own observatory, which Tycho called Uraniborg, the Castle of the Heavens. It had no telescopes — they weren’t invented yet.

He had several assistants, all of which he treated like servants, to help him with his observations. Among them was Johannes Kepler, who would later become one of the most important astronomers of all time, as we shall see. (Kepler was a pretty strange person himself, but a description of his quirky character will have to wait for another day.)

Uraniborg boasted gigantic quadrants to measure the exact locations of the stars and planets. He amassed a gigantic pile of planetary-positional data. But he shared that data with no one, not even his assistants.

Brahe ran his observatory like he was the ruler of a very small kingdom. He hosted lavish parties for potential patrons of his astronomical research. Its extensive grounds included wild animals. Notable among them was a trained moose. Perhaps it was an elk. Again, the historical sources are at odds. In any case, the moose (or elk) later died from drinking too much beer while on loan to a potential financial patron of Brahe’s astronomical research.

His measurements of planetary motion became his most lasting contribution to astronomy.

In those days, virtually every astronomer believed in the Aristotelian model of the universe. Earth was at the center of the cosmos. The “planets,” a term that included the sun and moon, orbited around Earth in perfect circles and all moved at a steady, unchanging speed.

Above the planets, the stars existed in their own “sphere.” Their position remained constant with respect to each other, and the number of stars never changed.

Tycho’s observation of the 1572 supernova dispelled the notion that the starry sphere was unchanging. Also, his data clearly showed that the old Aristotelian model was incorrect. However, he could not disabuse himself of the notion that Earth was at the center of things. Brahe cleverly came up with a model that explained his data pretty well and still kept Earth at the center.

His model of the universe put Earth at the center. The moon and sun orbited Earth. Everything else orbited the sun.

It was an elegant solution based on hard observations, but it still didn’t quite fit the data.

The actual solution would have to wait until after his death, which was as strange as his life.

Brahe collapsed during one of his many lavish banquets. He had guests, and he considered it extremely impolite to rise from the table to relieve himself, especially when rich potential patrons were present. Thus it was that he died of a burst bladder sitting at dinner.

Kepler took advantage of his demise by absconding with Brahe’s wealth of planetary data. It was theft, pure and simple, but Kepler can be excused because he used those data to fundamentally change the way that we look at the universe.

Kepler was fundamentally at odds with Brahe and his Earth-centered solar system because he believed in the new Copernican theory that the planets, Earth included, orbited the sun. However, the Copernican model did no better at explaining Brahe’s actual, measured planetary positions than Brahe’s Earth-centered model.

In both the old Aristotelian model and the Copernican model, the orbits were all perfect circles and the planets moved at a steady, unchanging speed. Perhaps the circles were to blame.

Kepler tried every possible kind of orbit until he hit upon the ellipse, a kind of stretched-out circle, an astounding revelation that exactly predicted the positions of the planets.

As a result, Kepler is remembered as the astronomer who nailed the sun-centered model into place. But he couldn’t have done it without stealing Brahe’s detailed data.

While he was alive, Brahe’s claim to fame was his detailed observation of his supernova, which is still called Tycho’s Supernova to this very day despite the fact that he was not the only person (nor even the first person) to observe it.

Kepler couldn’t top that accomplishment. Or could he? In 1604, Kepler observed the second supernova in a generation. Kepler’s Star, as it is sometimes called, was easily visible in broad daylight for three weeks.

Kepler was not the first person to observe the supernova. In fact, cloudy weather prevented him from observing it until three weeks after it was visible. But Kepler doggedly observed it, sans telescope, for a solid year after its appearance until it faded from naked-eye visibility. His careful record of its diminishing brightness stands as one of the great observational feats of all time.

Since then, no supernovae have been observed in our Milky Way galaxy.

Perhaps your destiny is not so grand as Kepler’s or as weird and grand as Tycho Brahe’s. But it is certainly worth going out into the clear, crisp nights of early summer to drink in the sky’s splendors. Perhaps your lucky star is out there, just beyond the tip of your nose, waiting.

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By Tom Burns

Stargazing

Tom Burns is the former director of the Perkins Observatory in Delaware.

Tom Burns is the former director of the Perkins Observatory in Delaware.