Reference
- Aristarchus of Samos (c.310-c.230 BC)Greek astronomer and mathematician who measured the distances of the Sun and Moon, and who is also cited as the first astronomer to propound a heliocentric theory. Aristarchus reckoned the Sun's and Moon's distances by measuring the apparent angle between the Earth and Sun during the first quarter Moon, when the Moon-Sun angle is 90°. Though his method was mathematically valid, the exact moment at which the Moon was 50% illuminated proved very difficult to measure in practice, and any slight error in its value would introduce gross errors in the final result. Aristarchus observed the Sun-Earth-Moon angle as 87°, determining that the Sun was twenty times as far from the Earth as the Moon, and hence was twenty times the actual size of our natural satellite. Because the actual angle at first quarter is 89° 50′, the Sun is really about 400 times as distant, but Aristarchus' result, announced in his work On the Sizes and Distances of the Sun and Moon, nevertheless demonstrated that the Sun is a much more distant celestial object than the nearby Moon.
- Copernicus, Nicolaus (1473-1543)Nicolaus Copernicus (in Polish, Mikotaj Kopernik) was a Polish mathematician and astronomer, best known for his heliocentric theory of the solar system. The heliocentric theory, also known as the Copernican system, holds that the sun is at the center of the universe, and that the earth rotates on an axis and revolves around the sun. Copernicus published his theory in De Revolutionibus Orbium Coelestium, often considered to be the starting point of the scientific revolution.
- Galileo GalileiItalian astronomer, physicist and mathematician. He was one of the first to use the telescope for astronomical observations, discovering mountains and craters on the Moon, and four satellites of Jupiter now known as the Galilean satellites. He observed the phases of Venus, and studied sunspots, from whose motion he deduced that the Sun rotates. Galileo concluded that ARISTOTLE's picture of the world, still widely believed in his time, was wrong and he championed COPERNICUS' heliocentric theory. This brought him into conflict with the Catholic Church and led to his trial and house arrest for the last eight years of his life.
- Hubble, Edwin P(owell)(born Nov. 20, 1889, Marshfield, Mo., U.S.—died Sept. 28, 1953, San Marino, Calif.) U.S. astronomer. He earned a degree in mathematics and astronomy at the University of Chicago, then made a brief foray into law before returning to astronomy. After earning his Ph.D., he began working at Mount Wilson Observatory. In 1922–24 he discovered that certain nebulae contained Cepheid variable stars; he determined that these were several hundred thousand light-years away (outside the Milky Way Galaxy) and that the nebulae they were in were actually other galaxies. In studying those galaxies, he made his second remarkable discovery (1927): that the galaxies were receding from the Milky Way at rates that increased with distance. This implied that the universe, long considered unchanging, was expanding (see expanding universe); even more remarkable, the ratio of the galaxies’ speed to their distance was a constant (see Hubble’s constant). Hubble’s original calculation of the constant was incorrect; it made the Milky Way larger than all other galaxies and the entire universe younger than the surmised age of Earth. Later astronomers determined that galaxies were systematically more distant, resolving the discrepancy.
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Perspectives
Galileo and 400 Years of Telescopic Astronomy
In 1609 Galileo first used his telescope to kick start the science of observational astronomy - an event that proved to be of enormous historic, scientific, and cultural importance. Galileo and 400 Years of Telescopic Astronomy will feature the life and achievements of Galileo, around which has pivoted the story of four centuries of telescopic astronomy. The book will detail how astronomy has progressed through four centuries and contain glimpses of future space research and astronomy goals. Uniquely, interwoven with the text will be a range of practical projects for backyard astronomers in which to participate, projects that serve to illustrate many of Galileo's scientific discoveries.
Edwin Hubble
An exploration of Hubble's contributions, his personal successes, & the activities & views that sometimes annoyed others inside & outside the scientific community.
Galileo
The opening of the archives of the Congregation of the Doctrine of the Faith, which occurred in 1998, brought to light important new documents on aspects of the trial of Galileo and on steps taken by the Church in 1757. This third edition looks at the new information which emerged.
The Book Nobody Read
In the spring of 1543 as the celebrated astronomer, Nicolaus Copernicus, lay on his death bed, his fellow clerics brought him a long-awaited package: the final printed pages of the book he had worked on for many years: De revolutionibus (On the Revolutions of the Heavenly Spheres). Though Copernicus would not live to hear of its extraordinary impact, his book, which first suggested that the Sun, not the Earth, was the center of the universe, is today recognized as one of the most influential scientific works of all time--thanks in part to astrophysicist Owen Gingerich. Four and a half centuries after its initial publication, Gingerich embarked on an epic quest to see in person all extant copies of the first and second editions of De revolutionibus. He was inspired by two contradictory pieces of information: Arthur Koestler's claim, in his bookThe Sleepwalkers, that nobody had read Copernicus's book when it was published; and Gingerich's discovery, in Edinburgh, of a first edition richly annotated in the margins by the leading teacher of astronomy in Europe in the 1540s. If one copy had been so quickly appreciated, Gingerich reasoned, perhaps others were as well--and perhaps they could throw new light on a hinge point in the history of astronomy. After three decades of investigation, and after traveling hundreds of thousands of miles across the globe--from Melbourne to Moscow, Boston to Beijing--Gingerich has written an utterly original book built on his experience and the remarkable insights gleaned from examining some 600 copies of De revolutionibus.
Chinese and Other Non-Western Constellations
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Study the constellation patterns of ancient China, which influenced those of India and Arabia. Professor Schaefer dates the origin of the Chinese star groups called lunar lodges, and he samples southern constellations conceived by cultures in South America, and Australia.
The Genius of Hipparchus
- Kanopy This link opens in a new windowConsidered the greatest astronomer of the ancient world, Hipparchus created a thousand-star catalog and discovered precession, the eons-slow rotation of the fixed stars around the ecliptic. Did this remarkable discovery give birth to the Mithraic religion, which rivalled Christianity?
Revolution in the Heavens
- Kanopy This link opens in a new windowDrawing on ideas and observations of Nicolaus Copernicus and Tycho Brahe, Johannes Kepler achieved a great insight about gravity by discovering three laws of planetary motion, relating to the mathematics of orbits. The cause of planetary motion, he determined, must lie in the sun.
Online Resources
- Determination of the Sun's and the Moon's sizes and distances: Revisiting Aristarchus' methodWe have investigated the practicability of Aristarchus' method of determining the Sun's and the Moon's sizes and distances from Earth using a simple 8-in. telescope and a digital camera. Combining our astrometric observations made on October 20, 2012 with data from the lunar eclipse of June 15, 2011, and adopting a proper statistical approach, we obtain the two distances with errors of a few percent for the Moon and about 10% for the Sun. We also explain quantitatively why Aristarchus and his contemporaries, though able to measure the Moon's size and distance acceptably, could not be successful in determining the Sun's size and distance. Our experiment can be carried out in small semi-professional or amateur observatories and can be performed in an astronomy lab class.
- Teaching physics with Hubble’s law and dark matterPhysics instructors can enrich, enliven, and enhance their courses with conceptually rich cosmology content. In this paper, we specifically discuss how instructors can integrate lessons on Hubble’s law (as it relates to the expansion of the universe and dark energy) and spiral galaxies’ rotation curves (as they relate to the presence of dark matter) into an introductory, college-level course on mechanics. These cosmology topics intersect with the content of introductory physics in a number of areas, such as students’ abilities to read and interpret graphs and their conceptual understandings of both kinematics and dynamics. Throughout this paper, we draw upon the results from, and research-validated curricula informed by, physics and astronomy education research. In particular, we feature the results from a national study we recently completed with introductory college-level general education astronomy students on the teaching and learning of cosmology.
How Ancient Astronomy Ended
- Kanopy This link opens in a new windowReview the state of astronomy in 1500. Then chart the revolution sparked by Copernicus's heliocentric theory of the Sun and planets. Learn how Copernicus was the last of the ancient astronomers, succeeded by the founders of modern science, including Tycho, Kepler, and Galileo.