## If you love the cosmos, you have to know at least one of these names, which went down in history for having contributed great legacies to science as the most important astronomers.

Life itself is an unresolved unknown that we have tried to answer from different angles, and what better since more positions are synonymous with a much broader picture? Science today is so specialized that we forget that there was a time in history when philosophy and science rubbed against each other almost on the same line. The segregation between the philosophical reflections of humans and science does not exist. Proof of this is the greatest astronomers who began their careers looking at the immensity of space and wondering who we are in this cosmic void.

## The most important astronomers in history

## Claudius Ptolemy

We owe him the first models of the universe since he was the first to propose a hypothesis that explained the natural phenomena of the Earth. Ptolemy believed that the Earth was immobile and occupied the center of the universe, and although today we know that this is not so, his hypothesis served to develop new models.

His greatest contribution is contained in the *Almagest*, the most important astronomical treatise of his time, where he stipulated his catalog of stars, which included 48 constellations, among which were the 12 zodiacal constellations.

## Nicolaus Copernicus

Although there were supporters of the heliocentric model even before Copernicus, it was not until Nicolaus Copernicus that the idea that the Earth was not the center of the Universe became more relevant. The Polish astronomer fervently defended that it was the Sun that was placed at the center and rather our Earth and the other planets revolved around it.

His masterpiece *De revolutionibus orbium coelestium *of 1543, contains a lecture on the heliocentric model, as well as an accurate description of the orbital motions of the planets and the Moon around the Earth. His greatest book and contribution are considered the beginning of modern astronomy.

## Galileo Galilei

Copernicus laid the foundations of modern astronomy, but it was Galileo Galilei who brought it to its peak, so much so that he is considered the father of modern astronomy, physics, and science. Although such a title cost him house arrest for life, he defended the heliocentric model and contradicted the theories of Aristotelian physics, thus earning him the attention of the religious Inquisition.

Galileo broke the principles under which physics and the universe were understood in his* Dialogo sopra i due massimi sistemi del mondo Tolemaico, e Coperniciano* published in 1632. He built the first powerful telescope and discovered four moons of Jupiter: Ganymede, Europa, Callisto, and Io.

## Johannes Kepler

His major contributions include the laws of motion of the planets that Isaac Newton later proved. These three laws mathematically describe the motion of the planets in their orbits around the Sun, he was the first to describe an elliptical trajectory instead of a perfectly circular one. He also discovered that the speed of the planets is not constant.

## Isaac Newton

Classical physics has its foundation in the contributions of Sir Isaac Newton who not only left a great legacy in astronomy but also optics, calculus, and even played the role of detective in finding the greatest counterfeiter of coins in England, for which he has been crowned as the most intelligent person of all humanity.

n his *Principia* of 1687, he established his three laws of motion that govern all objects on Earth and that for many centuries were applied to the motions of the stars and explained the theory of gravitational attraction, until Albert Einstein arrived. He also carried out studies in mathematics, creating the systems of integral and differential calculations, in addition to discovering the behavior of light and its decomposition into the seven colors of the rainbow.

## William Herschel

Together with his sister Carolina Herschel, he dedicated much of his life to the construction of telescopes with which he managed to discover many celestial bodies including planets, moons, stars, and nebulae. Herschel was the first astronomer since antiquity to discover a planet in the Solar System, in 1781 he classified the planet Uranus as one of the major planets.

Other discoveries made by Herschel include two of Uranus’ moons and two Saturnian moons, as well as a total of 80 pairs of groups of stars orbiting around a common center of gravity. He also published two catalogs describing a total of 7,500 nebulae.

## Henrietta Swan Leavitt

Today it is common to hear about the distances of objects that are light years away from us, but in the early 20th century distances were really uncertain. Henrietta changed the way astronomers observe the sky thanks to her discovery of the luminosity of stars. While examining photographic plates to catalog the brightness of stars, she realized that there was a direct correlation between the pulsating luminosity of stars known as Cepheids and the pulsation frequency. Thanks to this, Cepheid stars can nowadays be used as distance markers in the Universe, the reason why we know the distance between our Earth and extremely distant objects.

## Albert Einstein

Just as Galileo Galilei was in his time, Einstein also became a revolutionary in science, as he masterfully refuted everything we knew about space. On November 25, 1915, Einstein presented before the Prussian Academy of Sciences his now famous *Theory of General Relativity*, with which he completely broke the physics of space and which is still valid today.

Although it was not well received by a group of scientists, over the years the theory was proven thanks to a solar eclipse and with this, Pandora’s box was opened where several discoveries took place. The discovery of black holes and other space-time deformations was only possible thanks to Einstein.

## Stephen Hawking

The last great astrophysicist modern man has seen, Stephen Hawking is known for his work with black holes, Hawking radiation, and the understanding of the Universe. Thanks to his contributions to black holes, it was possible to prove that the Universe began with a huge explosion, the so-called Big Bang.

Hawking looked at the cosmos like no one else and laid the foundations for a theory of quantum gravity. The mathematical expressions used to explain gravity and quantum physics are not compatible with each other. But Hawking defied all theoretical limits and laid the foundations for the unification of general relativity, the theory of gravitation and spacetime, and quantum mechanics, which is still under development.

*Story originally published in Spanish in **Ecoosfera*