• 200

# Aristotle

Aristotle argued that the universe is spherical and finite. Aristotle believed that each planet followed the path laid out by a certain number of spheres.
• 200

# Aristarcus of Samos

Aristarcus of Samos had a belief that the Earth revolves around the Sun. One of his best known works attempting to determine the sizes and distances of the sun and moon.
• 200

# Eratosthenes

First person to calculate the circumfrence of the Earth.
He also created a map of the world.
• 200

# Pythagros

Created pythaorgean theorem. Pythagoras was also credited with devising the tetractys, the triangular figure of four rows, which add up to the perfect number, ten.
• 200

# Hipparchus

Hipparchus is considered the greatest ancient astronomical observer. He was the first whose quantitative and accurate models for the motion of the Sun and Moon survive.
• Feb 19, 1473

# Copernicus

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. His book is regarded as the start for modern astronomy
• Dec 14, 1546

# Tycho Brahe

Tycho is credited with the most accurate astronomical observations of his time, and the data were used by his assistant, Johannes Kepler, to derive the laws of planetary motion. On 11 November 1572, Tycho observed a very bright star, now named SN 1572, which had unexpectedly appeared in the constellation Cassiopeia.
• Feb 15, 1564

# Galileo Galilei

Galileo made original contributions to the science of motion through an innovative combination of experiment and mathematics. For Galileo, the tides were caused by the sloshing back and forth of water in the seas as a point on the Earth's surface speeded up and slowed down because of the Earth's rotation on its axis and revolution around the Sun.
• Dec 27, 1571

# Johannes Kepler

Johannes Kepler's first major astronomical work was the first published defense of the Copernican system. Kepler also found a formula relating the size of each planet’s orb to the length of its orbital period: from inner to outer planets, the ratio of increase in orbital period is twice the difference in orb radius.
• # Isaac Newton

His Philosophiæ Naturalis Principia Mathematica published in 1687, is one of the most important scientific books ever written. Newton built the first practical reflecting telescope.
• # Anne Jump Cannon

Know for the first serious attempt to organize and classify the stars based on the tempatures. Her work was theory laced but simplified.
• # George Hale

Hale was a driven individual who worked to found a number of significant astronomical observatories, including Yerkes Observatory, Mount Wilson Observatory, Palomar Observatory, and the Hale Solar Laboratory. Hale suffered from neurological and psychological problems, including insomnia, frequent headaches, and schizophrenia, claiming to have regular visits from an elf who advised him on his work. He would spend months at a time in sanitariums.
• # Henrietta Swan Leavitt

Leavitt's discovery of the period-luminosity relation of Cepheid variables radically changed the theory of modern astronomy, an accomplishment for which she received almost no recognition during her lifetime. The asteroid 5383 Leavitt and the crater Leavitt on the Moon are named in her honor.
• # Albert Einstein

Introuduced the theory of relativity Einstein postulated that light itself consists of localized particles.
• # Edwin Hubble

He discovered the degree of doppler shift. He also discovered that the universe goes beyond the milky way.
• # Gerard Kuiper

Kuiper discovered two natural satellites of planets in the solar system, namely Uranus's satellite Miranda and Neptune's satellite Nereid. He also discovered carbon dioxide in the atmosphere of Mars and the existence of a methane-laced atmosphere above Saturn's satellite Titan in 1944.
• # Bengt Georg Daniel Stromgren

He found that the chemical composition of stars was very much different than previously assumed.
In the late 1930s, he found the relative abundance of hydrogen to be nearly 70 %, and helium to be about 27 %.
• # 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. He studied stellar structure, including the theory of white dwarfs, during the years 1929 to 1939, and subsequently focused on stellar dynamics from 1939 to 1943.
• # Grote Reber

In the summer of 1937, Reber decided to build his own radio telescope in his back yard in Wheaton. Reber's first receiver operated at 3300 MHz and failed to detect signals from outer space, as did his second, operating at 900 MHz.
• # James Van Allen

The Van Allen radiation belts were named after him. On December 29, 1947 Van Allen elected chairman of the V-2 Upper Atmosphere Panel.
• # Sir Fred Hoyle

He observed that one particular nuclear reaction, the triple-alpha process, which generates carbon, would require the carbon nucleus to have a very specific energy for it to work. He found the idea that the universe had a beginning to be philosophically troubling, as many argued that a beginning implies a cause, and thus a creator .
• # E. Margaret Burbidge

She started research in collaboration with her husband Geoffrey Burbidge, Fred Hoyle and William Alfred Fowler. The resulting theory was called the B2FH theory after the participants. In 1972 she turned down the Anne Jump Cannon award because it was only awarded to women.
• # Eugene Shoemaker

Co-discovered comet Shoemaker-levy 9. Started a systematic search for Earth orbit crossing asteroids.
• # Thomas Mutch

He published two books about the geology of the Moon and of Mars. As head of the Viking surface photography team, he is quoted as commenting on the first pictures: "This is just an incredible scene. It looks safe and very interesting." A crater on Mars was named in his honor, and the Viking 1 lander was renamed "Thomas A. Mutch Memorial Station" in 1982.