Astronomy, the Greek derivative for the words ‘star law’, is the scientific study of celestial objects and phenomena that originate outside the Earth's atmosphere. Through Astronomy, we seek to understand the origin of the Universe and the Physical laws that define them.
Astronomy is one of the oldest sciences. Since the dawn of Human Civilization, our ancestors have been staring at the skies with wonder and awe and have tried to answer some of the profound questions of the Universe. Numerous Civilizations such as Indian, Egyptian, Greek and Babylonian have made significant contributions to our knowledge of the Universe. Names such as Aryabhatta and Bhaskaracharya are prominent when it comes to Indian Astronomy.
The present knowledge we have is due to the countless innovators that have contributed to the development and advancement of astronomy. Some of the key individuals include Nicolas Copernicus, Tycho Brahe, Johannes Kepler, Galileo Galilei, Isaac Newton, Albert Einstein, Edwin Hubble and Stephen Hawking.
It was only after the Renaissance that the theory of heliocentricity in astronomy, the idea that the Earth orbits the Sun rather than vice versa, began to acquire popularity. It was only after the invention of the Telescope by Galileo in the 1600s did Astronomy evolve into a Modern Science. The Refracting Telescope was invented in 1611 by Galileo Galilei, and he used this to take detailed observations of our Moon, which he revealed was mountainous, and observed Jupiter's four largest moons, now named the Galilean moons in his honor. Newton improved on Galileo's design, and invented the reflecting telescope, which is still used in optical telescopes to this day. During the early 1900s, Einstein came up with his theory of Relativity which revolutionized our understanding of Time and Space.
In astronomy, the main source that provides information about celestial bodies and other objects is the visible light or more generally electromagnetic radiation. Observational astronomy has been divided according to the observed region of the electromagnetic spectrum and hence we have Radio Astronomy, X-Ray Astronomy, Infrared Astronomy, Ultraviolet Astronomy and the like. Certain parts of the spectrum can be observed from the surface of the Earth, while other parts are only observable from either high altitudes or space. Orbital observatories such as the Hubble Space Telescope, named after Sir Edwin Hubble, have produced the best images; include extremely high-resolution photographs of other galaxies.
In the mid-1900s, it was discovered that the universe was expanding. This, along with other compelling evidence, led to the theory of the Big Bang, that the entire universe began as a point particle of extremely high density known as a Singularity (The point where the laws of Physics breakdown). Later observations of the cosmic microwave background radiation confirmed this, and the Big Bang continues as the primary theory of cosmological origins to this day.