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384 BCE
Aristotle
He studied under the great philosopher Plato and later started his own school, the Lyceum at Athens. He believed in a geocentric Universe and that the planets and stars were perfect spheres though Earth itself was not. He further thought that the movements of the planets and stars must be circular since they were perfect and if the motions were circular, then they could go on forever. -
100
Ptolemy
Ptolemy was an astronomer and mathematician. He believed that the Earth was the center of the Universe. The word for earth in Greek is Geo, so we call this idea a "geocentric" theory. Even starting with this incorrect theory, he was able to combine what he saw of the stars' movements with mathematics, especially geometry, to predict the movements of the planets. -
1473
Copernicus
When virtually everyone believed Earth was the center of the universe, Polish scientist Copernicus proposed that the planets instead revolved around the sun. Although his model wasn't completely correct, it formed a strong foundation for future scientists to build on and improve mankind's understanding of the motion of heavenly bodies. -
1546
Tycho Brahe
Alchemist, astrologer, astronomer, supporter of the geocentric (Earth-centered) theory of the Solar System. Designer and builder of astronomical instruments. Made some of the most accurate observations of planetary positions which would eventually prove useful to his predecessors. -
1564
Galileo
He provided a number of scientific insights that laid the foundation for future scientists.His investigation of the laws of motion and improvements on the telescope helped further the understanding of the world and universe around him. Both led him to question the current belief of the time — that all things revolved around the Earth. -
1570
Hans Lippershey
He laid claim to a device that could magnify objects three times. His telescope had a concave eyepiece aligned with a convex objective lens. One story goes that he got the idea for his design after observing two children in his shop holding up two lenses that made a distant weather vane appear close. -
1571
Johannes Kepler
He was a German astronomer who discovered three major laws of planetary motion. (1) the planets move in elliptical orbits with the Sun at one focus; (2) the time necessary to traverse any arc of a planetary orbit is proportional to the area of the sector between the central body and that arc (the “area law”); and (3) there is an exact relationship between the squares of the planets’ periodic times and the cubes of the radii of their orbits (the “harmonic law”). -
Giovanni Cassini
He was first observations of Saturn's moons. The Cassini spacecraft that launched in 1997 and plunged into the planet in 2017 was named after him. Cassini was an astronomer at the Panza Observatory from 1648 to 1669. He also served as a professor of astronomy at the University of Bologna. -
Sir Isaac Newton
Sir Isaac Newton contributed significantly to the field of science over his lifetime. He invented calculus and provided a clear understanding of optics. But his most significant work had to do with forces, and specifically with the development of a universal law of gravity. -
Difference between refracting and reflecting telescopes
A reflector telescope uses two mirrors instead of two lenses. Isaac Newton developed this telescope to combat chromatic aberration (a rainbow seen around some objects viewed with a refactor telescope). ... Light from an object enters the telescope tube and is reflected off a curved mirror at the end of the tube. -
William Herschel
He was a British astronomer, the founder of sidereal astronomy. He discovered the planet Uranus, hypothesized that nebulae are composed of stars, and developed a theory of stellar evolution. Herschel’s father was an army musician. -
Percival Lowell
From the study of Mars to the prediction of Pluto to the building of the observatory that bears his name, Percival Lowell enthusiastically dove headlong into the study of astronomy. Lowell decided to build an observatory. -
Ejnar Hertzsprung
He classified types of stars by relating their color to their absolute brightness—an accomplishment of fundamental importance to modern astronomy.The Hertzsprung-Russell diagram of stellar types was named for him. -
Albert Einstein
His work helps astronomers study everything from gravitational waves to Mercury's orbit. Einstein also made vain attempts to unify all the forces of the universe in a single theory, which he was still working on at the time of his death. -
Edwin Hubble
Hubble noticed a pulsating star known as a Cepheid variable inside each one. Cepheid are special because their pulsation allows for precise measurements of distance. Hubble calculated how far away each Cepheid lay — and thus how far to each nebula — and realized they were too distant to be inside of the Milky Way. -
Karl Jansky
Bell Labs wanted to investigate using "short waves" (wavelengths of about 10-20 meters) for transatlantic radio telephone service. Jansky was assigned the job of investigating the sources of static that might interfere with radio voice transmissions. -
Yuri Gagarin
Yuri Gagarin was the first person to fly in space. His flight, on April 12, 1961, lasted 108 minutes as he circled the Earth for a little more than one orbit in the Soviet Union's Vostok spacecraft. -
Kenneth Irwin Kellermann
The Owens Valley Radio Observatory was still being built, and Kellermann was one of the first to use its two-element interference, completing his Ph.D. under Gordon Stanley with measurements of spectra of both galactic and extra galactic radio sources. -
Sputnik
Tracking and studying Sputnik 1 from Earth provided scientists with valuable information. The density of the upper atmosphere could be deduced from its drag on the orbit, and the propagation of its radio signals gave data about the ionosphere. -
John Glenn
He was a United States Marine Corps aviator, engineer, astronaut, businessman, and politician. He was the first American to orbit the Earth, circling it three times. -
The Apollo Program
The Apollo program, also known as Project Apollo, was the third United States human spaceflight program carried out by the National Aeronautics and Space Administration, which succeeded in landing the first humans on the Moon. -
Neil Armstrong
Neil Armstrong was a NASA astronaut most famous for being the first person to walk on the moon. An accomplished test pilot, Armstrong also flew on the Gemini 8 mission. -
First Space Shuttle Flight
It was the fourth human spaceflight program carried out by the National Aeronautics and Space Administration, which accomplished routine transportation for Earth-to-orbit crew and cargo. -
Mars Pathfinder Expedition
It is an American robotic spacecraft that landed a base station with a roving probe on Mars in 1997. ... The mission carried a series of scientific instruments to analyze the Martian atmosphere, climate, geology and the composition of its rocks and soil. -
Cassini Orbiter
The Cassini–Huygens mission, commonly called Cassini, was a collaboration between NASA, the European Space Agency, and the Italian Space Agency to send a probe to study the planet Saturn and its system, including its rings and natural satellites.
