Introduction

If we know that the earliest observations of the sky were carried out by Mesopotamian civilizations (Egyptian, Greek, Arab world, etc.), the first significant scientific breakthrough of the modern era is attributed to the astronomer Nicolaus Copernicus, who, in the 16th century, developed a heliocentric model in which the Earth revolves around the Sun. This theory was progressively validated through the research and support of other astronomers, including Galileo. Galileo himself would also bring significant advances. Shortly after the telescope was invented, he improved its use to observe celestial bodies. Thanks to this instrument, he notably discovered Jupiter’s satellites and confirmed the phases of Venus, thus reinforcing the idea that not all celestial bodies revolve around the Earth. These discoveries marked a turning point in the history of astronomy and solidified the Sun's central position within the Solar System. Consequently, the concept of geocentrism — the belief that everything revolves around the Earth, began to gradually fall away. Following this, the work of Danish astronomer Tycho Brahe and his assistant Johannes Kepler (16th–17th centuries) further advanced our understanding of planetary motion. Brahe, thanks to highly precise observational instruments for his time (without using a telescope), managed to measure the positions of celestial bodies with unprecedented accuracy. Using these observations, Kepler formulated his famous laws of planetary motion, establishing that planets orbit the Sun in elliptical paths rather than circular ones. These discoveries definitively confirmed the validity of Copernicus's heliocentric model. In the 17th century, Galileo and Kepler's discoveries were given a crucial theoretical extension thanks to Isaac Newton (1642–1727). By formulating his law of universal gravitation, Newton demonstrated that the force holding the Moon in orbit around Earth is the same one keeping us firmly on the ground: every body exerts an attraction on others, proportional to its mass and inversely proportional to distance. This unifying theory laid the foundations of celestial mechanics, enabling precise calculations and predictions of planetary movements, comets, and other celestial bodies. Later, during the 18th and 19th centuries, the accuracy of observational instruments continued to improve, paving the way for modern observational astronomy. Astronomers discovered new planets (such as Uranus in 1781) and numerous other celestial objects (asteroids, nebulae, distant galaxies…), revealed by the constant progress of telescopes. The scientific mindset of the era also encouraged the development of spectroscopy, enabling researchers to determine the chemical composition of stars from the light they emit. Starting in the 20th century, humanity reached another significant milestone by shifting from observation to space exploration. Pioneers such as Konstantin Tsiolkovsky, Robert Goddard, and Hermann Oberth laid the groundwork for modern rocketry. The first space missions emerged in the 1950s and 1960s, with symbolic achievements including Sputnik 1 (1957, first artificial satellite in orbit), Yuri Gagarin’s flight (1961, first human in space), and humanity’s first steps on the Moon during the Apollo 11 mission (1969). Today, astronomical research and space exploration continue pushing the boundaries of our knowledge, whether through studying Mars, observing exoplanets, or detecting gravitational waves. One thing is certain: in space sciences, there will always be something new to discover...