astronomer argues for a changing cosmos
By R. Cowen
HVEN, Denmark, January 1578—Heavens! Could the teachings of Aristotle and other scholars all be wrong?
This placid island seems an unlikely place from which to challenge the prevailing view of the universe. But that's just what Danish astronomer Tycho Brahe has done. Two of his recent discoveries promise to shatter centuries of learned pronouncements that the cosmos is eternal and immutable. The findings suggest instead that chaos, turmoil, and change rule the universe.
Just 6 years ago, Tycho observed that stars can suddenly appear in the sky, blazing brighter than the planet Venus at its most luminous, and then fade from view. Now, he declares that the fuzzy, highly unstable objects known as comets reside in a region far beyond the moon, a region of the heavens thought to be unwavering and immutable.
The findings have all of Europe agog.
Tycho's odyssey began on the evening of Nov. 11, 1572. Walking back to his alchemy laboratory at Herrevad Abbey, near Copenhagen, the 26-year-old astronomer saw a brilliant white object that outshone Venus. Several of his servants and peasants confirmed his observations, he reported at the time.
The object, slightly northwest of the constellation Cassiopeia, remained for 18 months in a patch of sky where no star had ever been seen before. At times, it was so bright that observers could view it in broad daylight. It also changed from white to red to leaden gray.
Tycho and other astronomers scrambled to determine whether the new object moved across the sky. Any discernible motion would indicate the point-like object was not a star but an object nearer than the moon, within the so-called sublunary sphere. If so, the theories of Aristotle, Plato, and others who extoll the purity of the heavens could still hold.
The young astronomer had just built a new version of a sextant, a compass-shaped device that accurately measures the latitude and longitude of distant objects. Tycho's sextant, which features 5.5-feet-long arms joined by a brass hinge, is unsurpassed in detecting the subtle movement of distant objects, he says. When he applied the device to the bright apparition, he reports in his book De Stella Nova, it stood stock-still and so must be a star.
The startling discovery so intrigued King Frederick of Denmark that he bequeathed this island to Tycho for a new observatory. Still, the astronomer's finding cannot alone refute centuries of scholarly thought. A new study reported by Tycho just a few days ago, however, could force scientists to revise their long-held beliefs.
The newest drama began last November while Tycho was catching fish at dusk in one of his island's many ponds. He noticed what appeared to be a bright star in the western sky. As the evening grew darker, however, he saw that the object had a reddish tail, the telltale signature of a comet.
After sketching the comet, Tycho recorded its distance from two nearby stars in order to determine its position. Over the next few weeks, he diligently tracked the fading comet's motion and found that it has no measurable parallax—the extra motion of nearby objects due to Earth's movement through the heavens.
Indeed, in a report to the king, Tycho calculates that the comet must lie farther away than 230 times the radius of Earth, or more than four times the distance to the moon. There can be no doubt that the comet is a bona fide celestial body, beyond the sublunary sphere, and thus in direct conflict with the teachings of the ancients, Tycho says.
The king and others seem swayed by Tycho's careful measurements. Whether this comet of 1577 turns out to be an evil omen or a harbinger of good tidings remains to be seen, but it may spark a revolution in the way people view the cosmos.
From Science News, Vol. 156, No. 25 & 26, December 18 & 25, 1999, p. vii. Copyright © 1999, Science Service.