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Giants of Astronomy Aristarchus 310-230 B.C. was certainly both a mathematician and astronomer and he is most celebrated as the first to propose a sun-centered universe. He is also famed for his pioneering attempt to determine the sizes and distances of the sun and moon. According to his contemporary, Archimedes, Aristarchus was the first to propose not only a heliocentric universe, but also one larger than any of the geocentric universes proposed by his predecessors. Hipparchus was a Greek astronomer who lived between 190-120 B.C. He created the first accurate star map and kept a catalogue of over 850 stars with their relative brightness’s. Ptolemy Claudius Ptolemy (about 87-150) was a Greek astronomer and mathematician who wrote about his belief that all celestial bodies revolved around the Earth. His writings influenced people's ideas about the universe for over a thousand years, until the Copernican System (with a heliocentric solar system) was accepted. Nicholas Copernicus was a Polish astronomer who lived between 1473-1543. Before his time, people believed in the Ptolemaic model of the solar system, which maintained that the Earth was the center of the universe. Copernicus changed this belief when he introduced the heliocentric model, centered on the sun. He claimed that all the planets, including Earth, moved in orbits around the sun, and showed how this new system could accurately calculate the positions of the planets. Tycho Brahe was a Danish astronomer who lived between 1546-1601. For over twenty years, he made very accurate observations of the night sky, all without the aid of a telescope, which had not yet been invented. Tycho also built the world's first observatory and kept a star catalogue with over 1000 stars. Tycho's records were used by Johan Kepler to describe the orbits of planets around the sun and disprove the Ptolemaic theory. Johannes Bayer (1564-1617) was a Bavarian (German) astronomer who first named stars by assigning them to constellations and giving them Greek letters (alpha, beta, gamma, delta, etc.), in magnitude classes (by decreasing brightness). Bayer published Uranometria (a detailed star chart/catalog) in 1603. Hans Lippershey (1570?-1619) was a German-born Dutch lens maker who demonstrated the first refracting telescope in 1608, made from two lenses; he applied for a patent for this optical refracting telescope (using 2 lenses) in 1608, intending it for use as a military device Galileo Galilei was an Italian astronomer and physicist who lived between 1564-1642. He challenged Aristotle's proposition that heavenly bodies were divine and therefore perfect and blemish-free. Galileo was the first person to use a telescope to look at the heavens. He discovered sunspots, and craters and peaks in the moon. He discovered the large moons of Jupiter, which have been named for him. Galileo's work offended the Roman Catholic Church and he was sentenced to house arrest for the later years of his life. Today, he is remembered as a martyr for scientific truth. Johan Kepler was a German astronomer who lived between 1571-1630. He introduced three important laws of planetary motion and helped the Copernican model of the solar system gain general acceptance. Kepler inherited Tycho Brahe's observational data on Mars following Brahe's death and showed, mathematically, that Mars followed an elliptical orbit. This new revelation contradicted the age-old belief that heavenly bodies all moved in perfect circles. With Tycho Brahe's observations, Kepler set out to determine if the paths of the planets could be described with a curve . Christian Huygens was a Dutch physicist and astronomer who lived between 16291695. He found new methods for grinding and polishing lenses, making telescopes more powerful. Using a telescope he had made, Huygens first identified Saturn's rings and one of Saturn's moons. Huygens also invented the pendulum clock, increasing the accuracy of timekeeping, and proposed the wave theory of light. Isaac Newton was an English scientist and mathematician who lived between 16421727. He had one of the most brilliant minds the world has ever known. Legend has it that seeing an apple fall gave Newton the idea that gravity, the force that keeps us bound to the Earth, also controls the motion of planets and stars. Newton's contributions to science include the universal law of gravitation, the development of a whole new field in mathematics called calculus, and his famous three laws of motion. Ole Romer (1644-1710) was a Danish astronomer who, in 1675-1676, was the first person to demonstrate that the speed of light is finite. Romer did this by observing eclipses of Jupiter's moon Io as Jupiter’s distance from Earth varied through the year. He noticed that the observed period of Io's orbit differed by about 20 minutes; he concluded that this difference was due to the extra distance that the light had to travel to Earth. Edmond Halley was an English astronomer who lived between 1656-1742. Using historical records, his own observations, and Newton’s universal law of gravitation, he reasoned that the comets, which had appeared in 1456, 1531, 1607, and 1682, were one and the same. He then predicted the comet’s return about every 76 years. Although Halley died in 1742, the comet reappeared 16 years later, and today bears his name. William Herschel was born in Germany and lived in England as he worked as an astronomer. He lived between 1738-1822. He built high magnification telescopes that let him observe the heavens with greater detail. Herschel discovered the planet Uranus and advanced our understanding of nebulae, the hazy clouds that surround dying stars. He also founded stellar astronomy, the study of the region beyond our own solar system. Our modern sense of a galaxy’s shape is very similar to what Herschel had proposed hundreds of years earlier. Charles Messier (1730-1817) was a French astronomer who searched the skies for comets. He compiled a list of 103 fuzzy objects (nébuleuse sans étoile, or starless nebulosities) in space in order not to mistake star clusters, galaxies, and nebulae for comets (for which he was searching). The Messier list has been added to and now consisted of 35 galaxies, 30 open clusters, 29 globular clusters, 4 planetary nebulae, 7 diffuse nebulae, and two unconfirmed objects (which were mistaken for nebulae by Messier). Christian Doppler was an Austrian mathematician who lived between 1803-1853. He is known for the principle he first proposed in concerning the colored light of double stars in 1842. This principle is now known as the Doppler effect. He hypothesized that the pitch of a sound would change if the source of the sound were moving. He didn't test this hypothesis until 1845. To test his hypothesis, Doppler used two sets of trumpeters: one set stationary at a train station and one set moving on an open train car. Both sets of musicians had perfect pitch and held the same note. As the train passed the station, it was obvious that the frequency of the two notes didn't match, even though the musicians were playing the same note. This proved Doppler's hypothesis. Albert Einstein was a German physicist who lived between 1879-1955. Probably the most well known scientist of the twentieth century, Einstein came up with many original theories and invented modern physics. He is most famous for his theory of relativity, which makes bold statements about the nature of light and also shows the relationship between mass and energy. Einstein's accurate predictions on the link between gravity with space and time also made him a celebrity. His calculations predicted an expanding universe and he described space/time. Henrietta Swan Leavitt was born in Massachusetts in 1868. She became interested in astronomy in college. Unfortunately, she got sick after her graduation from college. She did recover from her sickness, though it did leave her almost completely deaf. But she hadn't forgotten astronomy! She observed stars and watched how variable stars changed in brightness. Henrietta is known for her discovery of a type of variable stars named Cepheid variables. Cepheid variables are stars that go through cycles of brightness and darkness. Henrietta found that when observing a Cepheid variable, she could relate the length of the brightness cycle to the size of the star. With this discovery, she was able to determine the distances between stars and the Earth. KIRCHOFF, GUSTAV Gustav Kirchoff (1824-1887) was a German physicist who realized that each element gave off a characteristic color of light when heated to incandescence. When separated by a prism, the light for each element had a specific pattern of wavelengths. Kirchoff, together with Bunsen, used his techniques to discover two new elements, cesium (1860) and rubidium (1861). Kirchoff found that when light shines through a gas, the gas absorbs some of the light, the same wavelengths of light that it would emit when heated. He applied his techniques to the Sun, explaining Fraunhofer lines. Edwin Hubble was an American astronomer who lived between 1889-1953. His observations of galaxies helped him develop the idea of an expanding universe, which forms the basis of modern cosmology, the study of the origin of the universe. He also discovered a relationship between a galaxy’s speed and its distance. The Hubble space telescope, currently on an observation project in space, bears his name. Karl G. Jansky (1905-1949) was an American radio engineer who pioneered and developed radio astronomy. In 1932, he detected the first radio waves from a cosmic source - in the central region of the Milky Way Galaxy. BELL, JOCELYN Susan Jocelyn Bell Burnell (1943- ) is an astronomer who discovered the existence of pulsars in 1967, while she was a graduate student at Cambridge University. A pulsar is a rapidly spinning neutron star that emits energy in pulses. Bell's graduate advisor (Anthony Hewish) was given a share of the 1974 Nobel Prize, but Bell was ignored. No one had any idea what these unusual objects were at the time, so the name little green men (LGM) was used. Soon, Thomas Gold suggested that pulsars were rapidly spinning neutron stars, the remnants of a supernova. CHANDRASEKHAR, S. Subrahmanyan Chandrasekhar (Born Lahore, India on Oct. 19, 1910 -Died Chicago, USA in 1995) was an Indian-American astrophysicist who studied stellar physics, evolution, and black holes. He realized that the fate of dying stars depended upon their mass, and above a certain point (1.4 times the mass of the Sun, now known as the "Chandrasekhar limit"), a star will undergo extreme collapse and not simply becomes a white dwarf. SAGAN, CARL Carl Sagan (1934-1996) was an American astronomer who discovered that the surface of Venus was extraordinarily hot and noxious (contrary to previous models of a mild Venusian surface). Sagan also showed that the universe has many organic (carbon-based) chemicals and that life is likely to exist throughout the cosmos. He was a great popularizer of astronomy, was involved in many NASA flights and SETI, and also pioneered the field of exobiology.