A very long time ago, people looked up at the sky and made stories about the sun, moon and stars. They believe the earth was flat and everything revolves around it. Then curious, clever folks observe the sky closely and started to ask questions. They used tools and mathematics to figure out how things in space really work. After that, our ideas about space began to change progressively. Now we able to send rockets and humans in space. Let’s discover how ideas of universe change from early ancient astronomy till modern astronomy.
Aristotle is the ancient Greek philosopher lived in 4th century B.C.E. He wrote a book called “On the Heavens”. In his book he marked few observations, he believed earth is stationary and at the center of the universe and sun, moon, stars, planets are revolved around the earth in circular orbit.
Aristotle also made few important observations such as
In the 2nd century C.E, Claudius Ptolemy, a Greco-Roman mathematician and astronomer, refined Aristotle’s geocentric model in his seminal work ‘Almagest’. He introduced concept of epicycles-small circular orbits planets made while orbiting the earth.
On based on Aristotle geo-centric idea Ptolemy build his own model. He placed earth at the center and all other bodies like sun, moon, stars and known planets at that time- Mercury, Venus, Mars, Jupiter, Saturn are placed around earth in eight spheres. The outermost sphere carried fixed stars. He said the planets moved in small circles called epicycles. These epicycles, in turn, moved in larger circles around the Earth. This complex system was like building a complicated puzzle to match the planet’s positions in the sky.
Ptolemy’s model could predict positions of bodies in sky but failed to predict these positions accurately. Through observation Ptolemy knows that, size, motion and brightness of these bodies are varied. He was aware of this flaw, still his model is generally accepted over a many centuries.
The 16th century made a radical breakthrough in our understanding of space with the work of Nicolaus Copernicus. He was a mathematician and astronomer. In his book “De Revolutionibus Orbium Coelestium” (On the Revolutions of the Celestial Spheres), Copernicus indicated a model in which the Sun was the center, not Earth, and all the planets including earth revolves around Sun. This idea became quite revolutionary and led the way to modern astronomy.
It is an idea that sounds a little crazy for its time, but it really does explain a lot of things that didn’t make sense before. For example, it explained why planets sometimes seem to move backwards in the sky and helped us understand the different lengths of seasons. Even though Copernicus had got the idea right, his proof was not good enough, and more time had to pass before people started believing it. More observations and research by other scientists had to be done before everyone agreed that the sun lay at the center of our solar system.
Galileo Galilei, an Italian astronomer in early 17th century challenged Aristotle and Ptolemy geo-centric model. During Galileo’s time, telescope was just invented. He started gazing stars and planets and saw things that no one had ever seen before !
He saw small satellites or moons are orbiting around planet Jupiter. By this observation, he comes on a conclusion that, everything did not have to orbit around the earth, as Aristotle and Ptolemy had thought. He also observes, planet Venus has a Phases just like moon. This helped to prove that the sun was at the center of our solar system, just like Copernicus said.
Galileo’s observations were very different from what most people thought and this is what got him into trouble. The Church didn’t like his ideas because they went against what they believed in. The work of Galileo changed the way people used to think about the universe, hence he has often been called the “father of modern science” because of his important discoveries.
Johannes Kepler was a smart scientist who lived around the same time as Galileo. He had worked on Copernicus’s theory and also studied the observations of astronomer named Tycho Brahe.
Keplar discovered that, the paths of the planets were not perfect circles, as Ptolemy had thought. Instead, planets revolved in oval shaped called ellipses. He further observed that the farther the planet was from the Sun, the more slowly it travelled, and the closer to the Sun, the faster.
Keplar’s Law of Planetary Motion
Kepler’s laws were a major breakthrough in astronomy. His discoveries were important in the sense that they gave insight into the way planets moves and how solar system work. Indeed, up to date, scientists and astronomers still use his laws of planetary motion.
Isaac Newton, one of the greatest scientists of all time, revolutionized our understanding of space in the late 17th century. In his work ‘Principia Mathematica Naturalis Causae’, Newton not only put forward theory but also developed mathematics requires to analyse how bodies move in space and time, known as laws of motion.
Newton formulated laws of universal gravitation. Newton realized that some force was holding things together. He called this force ‘Gravity’. He found that gravity is universal force and it works everywhere in the universe.
Newton’s law of universal gravitation states that every object in this universe attracts every other object by a force proportional to the product of their masses and inversely proportional to the square of the distance between them. Less technically, that means that heavier objects pull on each other more strongly than lighter objects do, and that those closer together pull on each other more strongly than do objects farther apart.
Newton’s law of universal gravitation explained, gravity is responsible to kept the planets in elliptical orbit around the sun, held the moon in elliptical orbit around the Earth, and kept us on the ground instead of floating away.
William Herschel was a German-born British astronomer in 18th century who actually changed our way of looking at the universe. He discovered the planet Uranus in 1781, the first planet found since antiquity and also the first ever discovered through telescope.
Herschel was a stargazer, mapping thousands of stars and nebulae with his large telescopes, which provided a framework for subsequent astronomical work. From his observations, two moons were reported for Uranus: Titania and Oberon. He also discovered infrared radiation, binary stars and published important catalogues of stars and nebulae.
One of Herschel’s main contributions to astronomy was that of the Milky Way galaxy. He assumed that it was a flat disk collection of stars, with our solar system close to its edge. This was a very radical idea against the general view of the Milky Way as a small cloud of stars.
The contribution of Herschel goes beyond astronomical discoveries. He was a pioneer of techniques for building and using telescopes and introduced substantial improvements into astronomical instrumentation. He builds world’s largest telescope at that time. He helped to build up astronomy as a strict science.
Edwin Powell Hubble was an American astronomer from 20th century. Hubble’s most significant contribution was his discovery of galaxies beyond our own Milky Way. He proved that many objects previously thought to be clouds of dust and gas and classified as “nebulae” were actually galaxies beyond the Milky Way.
In addition to his discovery of galaxies. Hubble also made crucial observations using his Hooker telescope, that supported the expanding universe theory. He measured the distance to nearby galaxies and found that they were moving away from us at a rate proportional to their distance. This relationship, known as Hubble’s Law, provided strong evidence for the idea that the universe is expanding outward.
His discoveries helped to establish the Big Bang theory, which states that the universe began from a hot, dense state and has been expanding ever since. His discoveries of galaxies beyond our own Milky Way and his evidence for the expanding universe are among the most significant contributions to cosmology in the 20th century.
From the mid-20th century, the space age begins with launch of first artificial satellite ‘sputnik 1’ by Soviet Union in 1957. This event initiated a space race and chain of space research activities all over the world and resulted in many scientific discoveries and technological inventions.
Key milestones of space age –
The Space Age did much for the great improvement in astronomy, astrophysics, and technology. It also inspired generations of scientists and engineers to explore the universe and push the envelope of human knowledge.
Probably the most exciting development in the last couple of decades is the discovery of so-called exoplanets, which are planets orbiting stars other than the Sun. Already, thousands have been identified by such instruments as Kepler and TESS, some of whom are potentially habitable.
These are crucial entities that hold keys to understanding structure and evolution in the universe. Scientist working to understand these mysterious entities, that make up majority of the universe’s mass and energy.
Black holes remain fascination corners for astronomers because of their makeup as spacetime areas from which the intensity of gravity is so high that nothing can be let out. The study of black holes makes available valuable information about extreme conditions that may prevail in the universe.
This has made the search for extraterrestrial life quite an attractive objective in the eyes of many astronomers. SETI, or Search for Extraterrestrial Intelligence, is actually a project monitoring all sorts of signals that come from outer space just in hopes of finding at least one from another civilization.
The modern space technologies have made enormous progress. The clarity of a space view is now unparalleled through the latest telescopes, including the James Webb Space Telescope. Spacecraft are moving closer to the sun than ever in history, with the Parker Solar Probe. Rovers and landers examine planets such as Mars and provide a huge amount of collected data. Besides, reusable rockets and the International Space Station lowered the cost and hassle of space missions tremendously. These are but a few of the many developments that have opened up new avenues for exploration and discovery—promising a future full of exciting possibilities.
From the philosophical speculations of Aristotle to the high-tech observations of modern astronomy, our understanding of space has grown immensely. Each age of discovery follows in the footsteps of the knowledge handed on by the previous one, deepening further and further into the cosmos. In this further exploration into the universe, we honour the legacy of the great thinkers and astronomers who have paved the way for the human intellect. The journey to understand space is only beginning, more exciting times of discovery and progress lie ahead.
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