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350 BCE
Earth model
Aristotle describes the geocentric (Earth- centered) model of the universe. In the model it shows a fixed spherical Earth which is in the center it is surrounded by concentric celestial spheres of planets and stars. The model explains the simple phenomena such as daily rise and set of celestial objects, -
200 BCE
Sun model
Aristarchus proposes a heliocentric (Sun-centered) model of the universe that is widely ignored -
150 BCE
Ptolemy Geocentric model
Ptolemy refines the geocentric model of the universe to try explain the retrograde (east to west) motion of the planets.
Ptolemy thought that all celestial objects including the planets, Sun, Moon, and stars orbited Earth. Earth, in the center of the universe, did not move at all. -
1520
Magnellianc Clouds
Ferdinand Magellan was the first European to observe the Magellanic Clouds during the first voyage around the world. Later on during the 20th century the clouds were recognised as the galaxies outside the Milky Way. -
1543
Copernican Heliocentric Model
Nicholas Copernicus published a paper presenting the heliocentric model of the universe. The model contained a number of improvements from the Aristarchus version. -
Giordano Bruno
Giordano Bruno was executed for believing in the universe being infinite and disregarding the geocentric theory. One of his crimes included the promtoing the heliocentrics model of the universe -
Astronomia Nova
Johannes Kepler Publishes Astronomia Nova. The book contains the results of the astronomer Johannes Kepler's ten-year-long investigation of the motion of Mars. Explaining the motion of the planets using the heliocentric model of the universe and the elliptical (oval shaped) orbits. -
Observation of Jupiters moons
Galileo Galilei first observed the Moons of Jupiter. They were the first objects found to orbit another planet. He discovered these moons using his rudimentary telescope on Jupiter and realized that it had 4 large moons orbiting it: Io, Europa, Ganymede, and Callisto. This was an important discovery because it demonstrated that Earth was not the center of the Universe as proven in the geocentric theory. -
Dialogue on the two world system is published
Galileo Publishes his dialogue on Two World Systems. Galileo masterfully demonstrates the truth of the Copernican system over the Ptolemaic one, proving, for the first time, that the earth revolves around the sun. -
Principia Mathematica is published
Isaac Newton Publishes Principia Mathematica, Over the three volumes he explained, for the first time ever, his three laws of motion and among other things explains the law of universal gravitation, he also defines scientific studies of the physical universe for the subsequent three centuries. -
Thomas Wright
Thomas Wright proposed that the Milky Way was actually a flat layer of stars, with our solar system immersed inside it and that the puffy motes of matter known as nebulae were separate galaxies of stars like the Milky Way. -
Discovery of Uranus
William Herschel discovers Uranus. He was using a telescope he built himself when he spotted a dim object. He watched it for years and determined it had to be a planet. This was the first planet to visible to the human eye. -
First map of the milky way is created
William Herschel was the first person to construct a map of the milky way. He used to record the relative positions of all such systems, He was, of course, assuming that the stars each have different brightness and were distributed in space. He took count of the stars over a small area of sky the number of stars visible would give him the area of the Milky Way in each direction. Thus formulating a map of the Milky Way. -
Observation of the Stellar Parallax
Friedrich Bassel was the first to stellar Parallax. He was the first to measure accurately the parallax, and hence the distance, of a star other than the Sun and the apparent movement of the stars due to the Earths movement around the sun. -
Discovery of Neptune
John Couch Adam discovered the planet Neptune. While sketching the moons of Jupiter with his newly discovered telescope, Galileo twice drew Neptune, which happened to be in conjunction with Jupiter in early 1613. It’s usually said that Galileo mistook Neptune for a star because of its slow movement. But though Galelios mistakes and the use of mathematics John Couch Adam was able to locate and discover the planet. -
Demonstration of Andromeda Nebula
Ernst Opik demonstrated that the Andromeda Nebula lies outside the Milky Way Galaxy. Ernest presented a method to estimate the distance of Andromeda using the measured velocities of its stars. His result placed the Andromeda Nebula far outside our galaxy at a distance of about 450,000 parsecs (1,500,000 light-years). -
Big Bang Theory is proposed
Georges Lemaitre proposes the Big Bang Theory. The theory is a scientific theory about how the universe started, and then made the stars and galaxies we see today. The theory suggests that the universe began as a giant explosion of energy. -
Evidence of the Universe Expanding
Edwin Hubble discovers evidence of the expanding universe, which helped to back up the big bang theory. With the benefit of improved telescopes, Hubble started to notice that the light coming from these galaxies was shifted a little towards the red end of the spectrum due to the Doppler effect (known as “redshift”), which indicated that the galaxies were moving away from us. Hubble showed that, in our expanding universe, every galaxy is rushing away from us. -
Discovery of Pluto
Clyde Tombaugh discovers the planet, Pluto. Tombaugh realized a movement across the field of a photo taken a month beforehand. After studying the object it came to be known as the 9th planet at the time. -
Further Evidence supporting Big Bang Theory
Arno Penzias and Robert Wilson discover cosmic microwave background radiation. They discovered the cosmic microwave background radiation (CMB), the ancient light that began saturating the universe 380,000 years after its creation. They had spotted the CMB, the predicted thermal echo of the universe's explosive birth. This discovery put the Big Bang theory on solid ground, suggesting that the cosmos did indeed grow from a tiny seed a single point about 13.8 billion years ago. -
First Humans to walk the surface of the moon
Neil Armstrong and Buzz Aldrin were the first human beings to walk on the surface of the moon. They landed on the moon in the Lunar Module. It was called the Eagle. He and Aldrin walked around for three hours. They did experiments. They picked up bits of moon dirt and rocks. They put a U.S. flag on the moon. They also left a sign on the moon. -
Pioneer 10
The pioneer 10 was the first spacecraft to leave the solar system. It was the first outer solar system mission, became the first probe not only to leave the inner solar system but also the first probe to be launched on an escape trajectory from the solar system and the first craft to visit the planet Jupiter. The spacecraft weighed 258 kilograms, -
Space craft Galileo
The Space Craft Galileo returns data suggesting that Europa has liquid oceans under its icy surface. It's believed that Europa has an iron core, covered by rock similar to the rock making up Earths crust. Due to Europa's distance from the sun it is very, very cold. Its outer surface is made up of ultra-cold ice: -162 degrees Celcius at the equator, and -223 degrees Celcius at the poles.
Under that ice most scientists believe there's a liquid ocean. -
Planet sized objects Discovered
Planet-sized objects Eris, Haumea, and Makemake are discovered in the Kuiper Belt. These objects are known as our solar systems Dwarf planets. -
Pluto is not a planet
The International Astronomical Union rules that Pluto is not a Planet. The IAU created a classification of a "dwarf planet," which is an object that meets planetary criteria except that it has not cleared debris from its orbital neighborhood. This definition meant that Pluto which was considered a planet at the time was reclassified as a dwarf planet.
