Nicolaus Copernicus (1473 - 1543)
Birthplace: Thorn, Poland
Copernicus busted the classical Greek theory of astronomy, which said the planets and celestial bodies orbited around the stationary Earth. His "heliocentric" model moved the sun to the center of the universe. Because of this, he is often called the "father of modern astronomy."
Interestingly, his skeletal remains were excavated by archeologists in Poland several years ago, and are set to be re-buried under the altar of Frombork Cathedral, where Copernicus was a member, later this year.
Galileo Galilei (1564 - 1642)
Birthplace: Pisa, Italy
Galileo has also been given a paternal nickname, "the Father of Modern Science."
Galileo ranks with Archimedes, Newton, and Einstein as one of the greatest scientists of all time. His discoveries, made with the crudest of equipment, were brilliant examples of scientific deduction. Galileo's studies of natural laws laid the groundwork for the experimental scientists who followed him.
Sir Isaac Newton (1643-1727)
Birthplace: Woolsthorpe-by-Colsterworth, Lincolnshire, England
His three laws of motion -- inertia, acceleration, and action and reaction -- remain a cornerstone of modern physics. His law of universal gravitation laid forth the theory that all particles in the universe exerted some gravitational force. In Newton's view, gravitational force was everywhere, from an apple falling from a tree to the moon being kept in orbit by its mutual attraction with Earth. While imperfect -- his law was later altered significantly by Einstein's theory of relativity -- Newton's conception of universal gravitation dominated physics for more than two centuries.
Stephen Hawking (1942- )
Birthplace: Oxford, England
After Albert Einstein, Stephen Hawking is probably the most famous physicist of all time. He became known for his study of certain physical characteristics of black holes, work that led to greater understanding of the origin of the universe. Hawking's A Brief History of Time: From the Big Bang to Black Holes (1988), which provides an overview of the origin and structure of the universe, was a best-seller.
Edmund Halley (1656-1742)
Birthplace: London, England
Halley is best known for his studies of the comet that bears his name. He observed it in 1682, calculated its orbit, and predicted its reappearance. As he had foretold, the comet reappeared in 1758; this was the first time that the reappearance of a comet had been correctly predicted.
Halley was a friend of Isaac Newton, and it was at Halley's urging and expense that Newton's Principia, the treatise that formulated the laws of gravitation, was published. Halley was also an inventor; he built a successful diving bell and found a way to supply divers with compressed air. Diving Halley contributed to other fields as well, including meteorology, optics, magnetism, and mathematics.
Edwin Hubble (1889-1953)
Birthplace: Marshfield, Missouri
Hubble revolutionized astronomy by showing that the universe is much larger than had been previously believed and by providing observational evidence for the theory of an expanding universe. One of his most important findings that the more distant a galaxy, the greater is the speed at which it is moving away from the Milky Way is now known as Hubble's Law.
In addition to the famous Hubble Space Telescope, Hubble's namesakes include an asteroid, a crater on Earth's Moon, a Planetarium, a highway, a high school, and an honorary medal.
Carl Sagan (1934-1996)
Birthplace: Brooklyn, New York
Sagan lead the charge to bring science into popular culture. He appeared frequently on television and wrote numerous best-selling books. Sagan became best known for his 1980 television series, Cosmos, and a book of the same name adapted from it. His study of human intelligence, The Dragons of Eden (1977), was awarded a Pulitzer Prize.