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# Aristotle (384 BC – 322 BC)

Philosipher who believed the earth was the center of the universe. Theorized planets were attached, not to the concentric spheres themselves, but to circles attached to the concentric spheres. Such ideas took on a new power as the philosophy of Aristotle was wedded to Medieval theology in the great synthesis of Christianity and Reason undertaken by philsopher-theologians such as Thomas Aquinas.
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# Aristarchus of Samos (230-310BC)

Aristarchus’ only extant treatise is “On the Sizes and Distances of the Sun and Moon.” In it he calculated the diameter of the Sun as about seven times the diameter of the Earth, thus estimating the Sun’s volume as about 300 times the volume of the Earth. His hypotheses are that the fixed stars and the Sun remain unmoved, and that the Earth revolves about the Sun in the circumference of a circle, the Sun lying in the middle of the orbit.
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# Pythagoras ( 570-c. 495BC)

Revered as a great mathematician, mystic and scientist, and he is best known for the Pythagorean theorem which bears his name. First to realize that Venus as an evening star, was the same planet as the morning star. Recognized that the orbit of the moon was inclined to the equator of the earth.
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# Hipparchus (190 BC – c. 120BC)

A Greek astrologer, astronomer, geographer, and mathematician of the Hellenistic period. Tried to come up with calculations of how far away the earth was from the moon. Thought to be the first to calculate a heliocentric system, but he abandoned his work because the calculations showed the orbits were not perfectly circular as believed to be mandatory by the theology of the time.
• 300

# Eratosthenes (276-195BC)

He was the first person to use the word geography and invented the discipline of geography as we understand it. He invented a system of latitude and longitude. first person to calculate the circumference of the earth by using a measuring system using stades, or the length of stadiums during that time period.
• # Copernicus

Renaissance astronomer and the first person to formulate a comprehensive heliocentric cosmology, which displaced the Earth from the center of the universe. His heliocentric model, with the Sun at the center of the universe, demonstrated that the observed motions of celestial objects can be explained without putting Earth at rest in the center of the universe. Copernicus was a mathematician, astronomer, physician, quadrilingual polyglot, classical scholar, translator, artist, and much more.
• # Tycho Brahe

A Danish nobleman known for his accurate and comprehensive astronomical and planetary observations. Observed a very bright star, now named SN 1572, which had unexpectedly appeared in the constellation Cassiopeia.
• # Johannes Kepler

A German mathematician, astronomer and astrologer, and key figure in the 17th century scientific revolution. Kepler's first Law: The orbit of a planet about the Sun is an ellipse with the Sun's center of mass at one focus. Kepler's second Law: A line joining a planet and the Sun sweeps out equal areas in equal intervals of time. Kepler's third Law: The squares of the periods of the planets are proportional to the cubes of their semi-major axes.
• # Galileo Galilei

His achievements include improvements to the telescope and consequent astronomical observations, and support for Copernicanism. Contributions to observational astronomy include the telescopic confirmation of the phases of Venus, the discovery of the four largest satellites of Jupiter, and the observation and analysis of sunspots. Galileo also worked in applied science and technology, inventing an improved military compass and other instruments.
• # Isaac Newton

Was a English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian. Built the first practical reflecting telescope. Developed a theory of colour based on the observation that a prism decomposes white light into the many colours that form the visible spectrum.
• # Albert Einstien

Born at Ulm, in Württemberg, Germany. In 1896 he entered the Swiss Federal Polytechnic School in Zurich to be trained as a teacher in physics and mathematics. In his early days in Berlin, Einstein postulated that the correct interpretation of the special theory of relativity must also furnish a theory of gravitation and in 1916 he published his paper on the general theory of relativity. Died on April 18, 1955 at Princeton, New Jersey.
• # Henrietta Swan Leavitt

One of the women human ‘computers’ brought in by Edward Charles Pickering to measure and catalog the brightness of stars in the observatory's photographic plate collection. She confirmed in 1912 that the variable stars of greater intrinsic luminosity actually Cepheid variables did indeed have longer periods, and the relationship was quite close and predictable. Also discovered more than 2,400 variable stars.
• # George Hale

Known for inventing the spectroheliograph. Used to make his discoveries of the solar vortices and magnetic fields of sun spots. Found significant astronomical observatories, including Yerkes Observatory, Mount Wilson Observatory, Palomar Observatory, and the Hale Solar Laboratory.
• # Annie Jump Cannon

One of the few women who went to college, studied mathematics and astronomy. Cannon discovered about 300 stars and classified the photographic spectra of about 325,000 more. Appointed Harvard Astronomer in 1938, first woman ever to be appointed.
• # Edwin Hubble

American astronomer who profoundly changed understanding of the universe by demonstrating the existence of galaxies other than our own, the Milky Way. Discovered that the degree of Doppler shift observed in the light spectra from other galaxies increased in proportion to a particular galaxy's distance from Earth.
• # Gerard Kuiper

Kuiper discovered two natural satellites of planets in the solar system, namely Uranus's satellite Miranda and Neptune's satellite Nereid. Discovered carbon dioxide in the atmosphere of Mars. Also discovered the existence of a methane-laced atmosphere above Saturn's satellite Titan in 1944.
• # Thomas Mutch

Published two books about the geology of the Moon and of Mars. A crater on Mars was named in his honor, and the Viking 1 lander was renamed "Thomas A. Mutch Memorial Station" in 1982
• # Bengt Georg Daniel Stromgren

A Swedish astronomer who did important research in stellar structure in the 1930s but is best known for his work on ionized gas clouds—H II regions—around hot stars. He surveyed H II regions and found relations between the gas density, the luminosity of the star, and the size of the “Strömgren sphere” of ionized hydrogen around it. He went to the United States and became director of the Yerkes and McDonald Observatories, and stayed there for six years.
• # Subrahmanyan Chandrasekhar

Won the 1983 Nobel Prize for Physics for key discoveries that led to the currently accepted theory on the later evolutionary stages of massive stars Studiedon the physical processes important to the structure and evolution of stars.
• # Eugene Shoemaker

Best known for co-discovering the Comet Shoemaker-Levy 9 with his wife Carolyn Shoemaker and David Levy. He was prominently involved in the Lunar Ranger missions to the Moon, which showed that the Moon was covered with a wide size range of impact craters. In 1969, he started a systematic search for Earth orbit-crossing asteroids, which resulted in the discovery of several families of such asteroids, including the Apollo asteroids.
• # Ancient Greek Astronomy (525BC)

Greek astronomy is also known as Hellenistic astronomy, while the pre-Hellenistic phase is known as Classical Greek astronomy. Most ancient civilizations watched the heavens as patterns in the sky that allowed the to know when the seasons changed. Counting phases of the moon or observing the annual variations of day length could, after many years of observations, serve as vital indicators for planting and harvesting times, and safe or stormy season for sailing.
• # Sir Fred Hoyle

An English astronomer and mathematician noted primarily for his contribution to the theory of stellar nucleosynthesis and his often controversial stance on other cosmological and scientific matters. Known primarily for the "Big Bang Theory
• # James Van Allen

Best known for his work in magnetospheric physics. After the success of the Soviet Union with Sputnik 1, Van Allen's Explorer spacecraft was approved for launch on a Redstone rocket. Van Allen was involved in the first four Explorer probes, the first Pioneers, several Mariner efforts, and the orbiting geophysical observatory.
• # E. Margaret Burbidge

Burbidge started studying astronomy in 1936 at University College, London, graduated in 1939 and received her PhD at University College in 1943. After ten years, in 1955, she finally gained access to the Mount Wilson Observatory, posing as her husband's assistant. Burbidge into one of the foremost and most influential personalities in the fight to end discrimination of women in astronomy.
• # Grote Reber

In the summer of 1937, Reber decided to build his own radio telescope in his back yard in Wheaton. Known for creating the radio telescope and making many outerspace discoveries.