These historical figures greatly contributed to our understanding of the universe today.

Interesting EngineeringBy Chris Young

© 12 | 9 of the World's Most Influential Early Astronomers

When we look up at the sky at night, we don't only see incredible natural phenomena playing out before our eyes, we also see an enormous tapestry of the past of our universe.
A sky is a time machine of sorts. It transmits the light of long-dead stars that are often millions of years old, allowing us to gather knowledge on the history of our universe and how it was formed.
The understanding of our universe is also possible thanks to a rich history of astronomers observing it and gradually adding to our knowledge of the way celestial objects move. Here is a list of some of the most influential early astronomers throughout history.

1. Aristarchus of Samos (310-230 BC)

Aristarchus of Samos was an ancient Greek mathematician and astronomer that is credited with having created the first-known map of our solar system, which placed the Sun at the center and Earth as a planet revolving the Sun.

9 of the World's Most Influential Early Astronomers
Source: Wikimedia Commons

Aristarchus also correctly predicted the rotation of Earth around an axis and correctly stated that other stars were similar in nature to the Sun, and were much farther away from Earth.

2. Eratosthenes (276-194 BC)

Eratosthenes became the Chief Librarian of the Great Library of Alexandria in ancient Greece. He is credited with having made some incredible calculations — especially considering the lack of tools at his disposal when compared with modern astronomers — that still hold up today.
Eratosthenes calculated the distance between the Sun and Earth and was only off by a few percents when compared with modern measurements. Similarly, he gave an impressively accurate measurement of the circumference of the Earth.
The ancient Greek astronomer is also recognized as having devised the need for a leap day, for having calculated the Earth's axis, and for having devised a map using meridians and parallels, which became the basis for indicating the position of stars in star charts that were used in astronomy and navigation.

3. Hipparchus (190-120 BC)

Hipparchus is credited as the founder of trigonometry and spherical trigonometry. The ancient Greek astronomer and mathematician used his work to develop his theories on lunar motions, allowing him to become the first person to successfully predict solar eclipses.

9 of the World's Most Influential Early Astronomers
Woodcut Illustration of Hipparchus observing the sky from Alexandria, Source: Wikimedia Commons

Aside from developing the first accurate models to describe the relative motions of the Sun and Moon, Hipparchus also compiled the first-star catalog in the Western world and accidentally discovered the precession of the equinoxes.

4. Gan De (Around 400-340 BC)

Gan De is the first individual, alongside his colleague Shi Shen, in known history to have compiled a star catalog. Though star catalogs are known to have been compiled by unknown Babylonian astronomers, Gan De is the first to have been recorded by history.
Also known as Lord Gan, Gan De made some of the first recorded observations of Jupiter. The Chinese astronomer and astrologer, who was born in the state of Qi, found ingenious ways to work around the technological limitations of the time. One method he used, for example, was to use a high tree branch to shield his vision from the glare of Jupiter, allowing him to make a naked-eye observation of one of Jupiter's moons.
A catalog compiled by Gan De and Shi Shen was discovered as part of the second century BC Mawangdui Silk Texts. It included surprisingly accurate movement observations of Jupiter, Venus, and Mars.

5. Ptolemy (100-170 AD)

Ptolemy's scientific treatise, Almagest, contains a comprehensive — for the time — star catalog, with detailed descriptions of 48 constellations as observed by the Greek astronomer and mathematician.

9 of the World's Most Influential Early Astronomers
Source: Wikimedia Commons

Much of Ptolemy's Almagest was usefully formatted in convenient tables that made it easy to calculate the past and future positions of celestial objects.

6. Aryabhata (476-550 AD)

Unfortunately, much of Aryabhata's prodigious talent has been lost to history. The Indian astronomer and mathematician was merely 23 years old when he wrote his most famous astronomical work, titled the Aryabhatiya. The original text was sadly lost, meaning that most of what is known about the astronomer's work is known today thanks to what was written down of it by contemporaries of his.
Amongst Aryabhata's achievements are the correct observation that the Earth rotates once around its axis every day, and that the visible movement of the stars and the Moon across the night sky occurs thanks to the rotation of the Earth. 
Aryabhata also correctly calculated the length of the day as being 23 hours, 56 minutes, and 4.1 seconds — this was correct to within a millisecond when compared with modern values. As for the correct value for the exact time of a year, Aryabhata calculated this as being 365.25858 days, which was only 3 minutes and 20 seconds over the length of a modern year.

7. Nicolaus Copernicus (1473-1543)

Though earlier astronomers had previously claimed that the Sun was the center of the solar system, Nicolaus Copernicus finally shattered the popularly believed and incorrect notion that all celestial objects revolved around the Earth.

9 of the World's Most Influential Early Astronomers
Source: Wikimedia Commons

Copernicus, of Poland, published his book, De Revolutionibus Orbium Coelestium ("On the Revolutions of the Heavenly Spheres") when he was 70 and on his death bed. Though his ideas didn't ignite the popular imagination until almost a hundred years later, his heliocentric model of the solar system is integral to our understanding of the universe today.

8. Galileo Galilei (1564–1642)

Galileo built on Copernicus's ideas in order to become one of the most important figures of the scientific revolution of the 17th century. Born in Pisa, Italy, Galileo was responsible for several scientific advancements on top of his work in astronomy; he developed the first pendulum clock and proved that all falling bodies fall at the same rate, regardless of mass.
He also experimented with and helped to refine the technology behind telescopes. Thanks to this technology, the Italian astronomer is credited with having discovered Jupiter's four largest moons, known today as the Galilean moons.
Galileo also helped popularize the Copernican heliocentric model of the solar system, which states that the Sun is at the center of our solar system. The Catholic church at the time forced Galileo to recant his theories about the heliocentric world model and kept him under house arrest for the last nine years of his life.

9. Isaac Newton (1642–1727)

Isaac Newton was a famously reclusive figure whose work almost never received the recognition it deserved. Thankfully, it did, and he is now considered one of the most influential figures in the history of science. Aside from having invented calculus, his creation of the three universal laws of motion and his invention of the theory of universal gravity changed the course of modern science.

9 of the World's Most Influential Early Astronomers
Source: Wikimedia Commons

Newton famously devised his theory for the law of universal gravitation after seeing an apple fall from a tree at his home at Woolsthorpe Manor in England. In 2010, a NASA astronaut carried a piece of the old but still standing, apple tree aboard the space shuttle Atlantis for a mission to the International Space Station. The aeronautics and space industry owes a great debt to Newton's universal laws of motion.
Incredible scientists like these might not come along often, but when they do, they build on the knowledge that is an accumulation of small discoveries made by the countless scientists that came before them. The work of Newton, Galileo and others built the foundations for the fascinating work of modern scientists such as Albert Einstein and Stephen Hawking. Could the next great scientist to fundamentally change our understanding of the universe be living amongst us now?
This article was originally published by Interesting Engineering.
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