coordinate system
A system that uses linear or angular quantities to designate the position of a point with respect to a selected reference position (called the origin) and an appro- priate reference surface or intersecting surfaces.See also CARTESIAN COORDINATES; CELESTIAL COORDI-
NATES; CYLINDRICAL COORDINATES; POLAR COORDINATE SYSTEM.
Copernican system
The theory of planetary motions pro- posed by NICHOLASCOPERNICUSin which all planets (includ-ing Earth) move in circular orbits around the Sun, with the planets closer to the Sun moving faster. In this system, the hypothesis of which helped trigger the scientific revolution of the 16th and 17th centuries, Earth was viewed not as an immovable object at the center of the universe (as in the geo- centric Ptolemaic system) but rather as a planet orbiting the Sun between Venus and Mars. Early in the 17th century JOHANNESKEPLERshowed that while Copernicus’s heliocen-
tric hypothesis was correct, the planets actually moved in (slightly) elliptical orbits around the Sun.
Copernicus, Nicholas
(Nicolaus) (1473–1543) PolishAstronomer, Church Official This Polish astronomer and church official triggered the scientific revolution of the 17th century with his book On the Revolution of Celestial
Spheres. Published in 1543 while Copernicus lay on his
deathbed, this book overthrew the Ptolemaic system by bold- ly suggesting a heliocentric model for the solar system in which Earth and all the other known planets moved around the Sun. His heliocentric model (possibly derived from the long-forgotten ideas of ARISTARCHUS OF SAMOS) caused
much technical, political, and social upheaval before finally displacing two millennia of Greek geocentric cosmology.
Nicholas Copernicus was born on February 19, 1473, in Torun, Poland. When Copernicus’s father died in 1483, his uncle (a powerful prince-bishop) raised him and provided the young man an extensive education. From 1491 to 1494 he studied mathematics at the University of Cracow, the leading institute of learning in Poland. Then he traveled to Italy in 1496 to broaden his knowledge and remained there for about a decade. He studied medicine in Padua (from 1501 to 1505). Later, however, he grew interested in astronomy because of lectures he heard while attending the University of Bologna. It was probably there that Copernicus first became fascinated with the little-known hypothesis of Aristarchus of Samos that the Earth revolved around the Sun. He also became a doctor of canon law as a result of his studies at the University of Fer- rara (1503).
The intellectual climate in late Renaissance Italy encour- aged bright students to investigate new ideas. The more Copernicus studied astronomy, the more uncomfortable he became with traditional Greek astronomy and its Earth-cen- tered model of the universe. For one thing, he considered the Ptolemaic system unnecessarily complex and incapable of predicting the positions of the planets over long periods. For another, he encountered the long-ignored but very intriguing thoughts of Aristarchus.
Around 260 B.C.E. this ancient Greek astronomer sug-
gested that he could more easily understand the observed motions of the planets if he assumed that they (including Earth) revolved around the Sun. He further suggested that since the stars appeared motionless (except for diurnal motion due to Earth’s rotation), they must be very far away. But the heliocentric hypothesis of Aristarchus was too revolu- tionary for the early Greeks. ARISTOTLE personally champi-
oned the then widely accepted geocentric model, and most ancient Greeks were culturally uncomfortable with the idea of a “moving” Earth. His book on the subject vanished in antiquity. The only contact Copernicus had with the helio- centric hypothesis of Aristarchus was probably through a brief mention of it in the writings of the great Greek mathe- matician Archimedes (ca. 287–212 B.C.E.). In any event,
Copernicus’s through investigation of geocentric Greek astronomy and its obvious deficiencies encouraged him to explore and validate the heliocentric hypothesis with a series of careful observations and calculations. His determined efforts in the early part of the 16th century would change sci- ence forever.
But caution about this new ideal was definitely the order of the day for Copernicus. In 1505 Copernicus returned to Poland and became a canon at his uncle’s cathedral in From- bork. Despite his formal religious education, he never became a priest. He also chose not to marry. Instead, he held the lucra- tive church position of canon until his death. Because of this position, however, he remained very prudent about openly
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advocating the revolutionary concept of the Sun at the center of the solar system. He reasoned quite correctly that this new model would create a direct conflict with church authorities. At that time ecclesiastical authorities regarded the geocentric model, which had been passed down from Aristotle and PTOLEMY, to be almost the equivalent of religious dogma. To
openly suggest otherwise could be regarded as a form of heresy—an offense often punished by death.
Yet Copernicus enthusiastically embarked on working out all the mathematical details of his new model. From 1512 to 1529, while still performing his clerical and administrative duties as a church canon, he made careful observations of planetary motions. He found that the inability of the geocen- tric model to predict planetary motions quickly disappeared if he assumed that Earth and the other planets actually revolved around the Sun. But Copernicus retained some of the features of the Greek model. For example, he assumed that the planets moved in perfect circular orbits around the Sun. JOHANNESKEPLERwould later correct this error by pos- tulating that the planets move in elliptical orbits.
To avoid open conflict with church authorities, Coperni- cus cautiously circulated his hand-written notes to a few close friends. In 1539 the Austrian mathematician Rheticus (Georg Joachim von Lauchen [1514–76]) arrived at Frombork to study under Copernicus. He reviewed the aging astronomer’s notes. Then, in a public test of the revolutionary concept, Rheticus published a summary of these notes in 1540 but was careful not to specifically mention Copernicus by name. This trial exposure of the heliocentric model actually occurred
without angering church authorities. On the contrary, scien- tific excitement about the Copernican hypothesis spread rapidly.
As a result Copernicus finally agreed to have Rheticus supervise the publication of his complete book De Revolu-
tionibus Orbium Coelestium (On the revolution of celestial
spheres). To avoid any potential doctrinal problems, Coperni- cus dedicated the book to Pope Paul III. Unfortunately, Rheti- cus left the final publication steps to a Lutheran minister named Andreas Osiander. The minister, mindful that Martin Luther himself firmly opposed the new Copernican theory, added an unauthorized preface to weaken the impact of its contents. In effect, Osiander’s unauthorized preface stated that Copernican theory was not being advocated as a descrip- tion of the physical universe but only as a convenient way to efficiently calculate the tables of planetary motions. The book (so modified) finally appeared in 1543. Historic legend sug- gests that Copernicus received the first copy as he lay on his deathbed. Fortunately, Johannes Kepler discovered the unau- thorized preface in 1609 and set the record straight. The cau- tious Polish astronomer certainly intended to change our model of the universe. Earth was definitely not the unmoving physical center of everything. It was just one of several plan- ets following predictable pathways around their parent star.
After his death on May 24, 1543, church authorities aggressively attacked the new heliocentric model and banned Copernicus’s book as heretical. His book remained on the church’s official list of forbidden books until 1835. For decades after the Copernican model appeared, the church used the Inquisition to attack those who supported the new concept. Through death, Copernicus mercifully escaped the harsh public punishment inflicted on some of his later sup- porters. In 1600, for example, the Inquisition burned one ardent Copernican, GIORDANOBRUNO, at the stake for his
beliefs. Ecclesiastical authorities condemned another Coper- nican, the famous Italian scientist GALILEOGALILEI, to house
arrest for the remainder of his life (from about 1633 to 1642). Nevertheless, the Copernican model survived and spawned a new era in learning and wisdom. Science histori- ans generally regard the pioneering work of Copernicus as the beginning of the scientific revolution.
Copernicus (spacecraft)
NASA’s Copernicus spacecraftwas launched on August 21, 1972. This mission was the third in the Orbiting Astronomical Observatory (OAO) Pro- gram and the second successful spacecraft to observe the celestial sphere from above Earth’s atmosphere. An ultraviolet (UV) telescope with a spectrometer measured high-resolution spectra of stars, galaxies, and planets with the main emphasis being placed on the determination of interstellar absorption lines. Three X-ray telescopes and a collimated proportional counter provided measurements of celestial X-ray sources and interstellar absorption between 1 and 100 angstroms (Å) wave- length. Also called the Orbiting Astronomical Observatory 3 (OAO-3), its observational mission life extended from August 1972 through February 1981—some nine and a half years. NASA named this orbiting observatory in honor of the famous Polish astronomer NICHOLASCOPERNICUS.
See also ORBITINGASTRONOMICALOBSERVATORY(OAO); ULTRAVIOLET ASTRONOMY.
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The universe according to Nicholas Copernicus. This simple heliocentric model of the solar system (using circular orbits) helped overthrow the long-standing geocentric cosmology of Aristotle and stimulated the great scientific revolution of the 17th century. (Drawing courtesy of NASA)
Cordelia
The small (about 30-km-diameter) innermost known moon of Uranus that orbits the planet at a distance of 49,770 km with a period of 0.335 days. This tiny satellite was discovered in 1986 as a result of the Voyager 2 space- craft encounter and subsequently named after the king’s daughter in William Shakespeare’s play King Lear. Orbiting close to Uranus, Cordelia acts as a shepherd moon for the planet’s epsilon ring—as does another tiny moon, Ophelia. An inclination of 0.08° and an eccentricity of 0.00026 fur- ther characterize the orbit of Cordelia. Sometimes called Uranus VI, UVI, or S/1986 U7.See also URANUS.
Córdoba Durchmusterung
(CD) The Córdoba Survey isa massive star catalog containing approximately 614,000 stars brighter than the 10th magnitude that was compiled at the Córdoba Observatory in Argentina. This cataloging effort was finally completed in 1930 and represents an analogous extension of the BONNER DURCHMUSTERUNG (BD) (Bonn Survey) to the Southern Hemisphere, especially the south
polar regions.
core
1. (planetary) The high-density central region of a planet. 2. (stellar) The very-high-temperature central region of a star. For main sequence stars, fusion processes within the core burn hydrogen, while for stars that have left the main sequence, nuclear fusion processes in the core involve helium and oxygen.coriolis effect(s)
1. The physiological effects (e.g., nausea, vertigo, dizziness, etc.) felt by a person moving radially in a rotating system, such as a rotating space station. 2. The ten- dency for an object moving above Earth (e.g., a missile in flight) to turn to the right in the Northern Hemisphere and to the left in the Southern Hemisphere relative to Earth’s sur- face. This effect arises because Earth rotates and is not, there- fore, an inertial reference frame.corona
The outermost region of a star. The Sun’s corona consists of low-density clouds of very hot gases (> 1 million K) and ionized materials.See also SUN.
Corona (spacecraft)
See DISCOVERER SPACECRAFT.coronal hole
A large region in the Sun’s corona that is less dense and much cooler than the surrounding areas. The open structure of a coronal hole’s magnetic field allows a constant flow of high-density plasma to stream out from the Sun. When coronal holes face in the direction of our planet, there is an increase in the intensity of the solar wind effects on Earth.See alsoSPACE WEATHER; SUN.
coronal mass ejection
(CME) A high-speed (10 to 1,000 km/s) ejection of matter from the Sun’s corona. A CME trav- els through space disturbing the solar wind and giving rise to geomagnetic storms when the disturbance reaches Earth.See alsoSPACE WEATHER; SUN.
cosmic
Of or pertaining to the universe, especially that part outside Earth’s atmosphere. This term frequently appears in the Russian (former Soviet Union) space program as the equivalent to space or astro-, such as cosmic station (versus space station) and cosmonaut (versus astronaut).cosmic abundance of elements
See ABUNDANCE OFELEMENTS(IN THE UNIVERSE).
Cosmic Background Explorer
(COBE) NASA’s CosmicBackground Explorer (COBE) spacecraft was successfully
launched from Vandenberg Air Force Base, California, by an expendable Delta rocket on November 18, 1989. The 2,270- kg spacecraft was placed in a 900-km altitude, 99°-inclina- tion (polar) orbit, passing from pole to pole along Earth’s terminator (the line between night and day on a planet or moon) to protect its heat sensitive instruments from solar radiation and to prevent the instruments from pointing directly at the Sun or Earth.
COBE’s one-year space mission was to study some of the most basic questions in astrophysics and cosmology. What was the nature of the hypothesized primeval explosion (often called the big bang) that started the expanding universe? What started the formation of galaxies? What caused galax- ies to be arranged in giant clusters with vast unbroken voids in between? Scientists have speculated for decades about the formation of the universe. The most generally accepted cos- mological model is called the big bang theory of an expand- ing universe. The most important evidence that this gigantic explosion occurred some 15 billion years ago is the uniform diffuse cosmic microwave background (CMB) radiation that reaches Earth from every direction. This cosmic background radiation was discovered quite by accident in 1964 by ARNO
ALLEN PENZIAS and ROBERT WOODROW WILSON as they were testing an antenna for satellite communications and radio astronomy. They detected a type of “static from the sky.” Physicists now regard this phenomenon as the radiation remnant of the big bang event.
The COBE spacecraft carried three instruments: the far- infrared absolute spectrophotometer (FIRAS) to compare the spectrum of the cosmic microwave background radiation with a precise blackbody source, the differential microwave radiometer (DMR) to map the cosmic radiation precisely, and the diffuse infrared background experiment (DIBRE) to search for the cosmic infrared background.
The cosmic microwave background (CMB) spectrum was measured by the FIRAS instrument with a precision of 0.03 percent, and the resulting CMB temperature was found to be 2.726 ± 0.010 kelvins (K) over the wavelength range from 0.5 to 5.0 millimeters (mm). This measurement fits very well the theoretical blackbody radiation spectrum predicted by the big bang cosmological model. When the COBE space- craft’s supply of liquid helium was depleted on September 21, 1990, the FIRAS instrument (which required the liquid heli- um cryogen) ceased operation.
The COBE spacecraft’s differential microwave radiome- ter (DMR) instrument was designed to search for primeval fluctuations in the brightness of the cosmic microwave back- ground, very small temperature differences (about 1 part in 100,000) between different regions of the sky. Analysis of
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DMR data suggested the presence of tiny asymmetries in the cosmic microwave background. Scientists used the existence of these asymmetries (which are actually the remnants of pri- mordial hot and cold spots in the big bang radiation) to start explaining how the early universe eventually evolved into huge clouds of galaxies and huge empty spaces. The COBE spacecraft pioneered the study of the cosmic microwave background.
NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) was launched in June 2001 and has made a map of the temperature fluctuations of the CMB radiation with much higher resolution, sensitivity, and accuracy that COBE. The new information contained in these finer fluctuations sheds additional light on several key questions in cosmology.
See alsoASTROPHYSICS;BIG BANG THEORY;COSMOLOGY;
WILKINSONMICROWAVEANISOTROPYPROBE(WMAP).