Astronomy is a branch of science that encompasses the study of extraterrestrial objects and phenomena. With the invention of the telescope and the discovery of the laws of gravity and motion in the 17th century, the study of astronomy became broader. These inventions were relatively used to expand the early catalog of objects studied in the field of astronomy, including objects in our own solar system and distant galaxies. These also became essential in noting and predicting the positions of the planets, the Moon, and the Sun for initial astrological and navigational purposes. Since the advent of the first scientific space probes in 1957, Earth was also studied from space. However, the thorough study of our planet remains the Earth Sciences domain.
Ancient astronomers have made numerous early observations and predictions. Historical records include several star charts that show great efforts to map the night sky and learn more about the dynamics of our universe. Examples of early observations and discoveries include the differentiation between a star and a planet. In the first and second BCE, Babylonian astronomers have tracked five points of light in the night sky. During their observation, they have noticed that these points of light moves differently than the other stars did. As a result, they concluded that there was something fundamentally different and that these light points were not stars at all. Historians and astronomers today believe that the Babylonians were among the first to identify planets that sometimes become visible to naked eyes such as Mercury, Venus, Mars, Jupiter, and Saturn.
Subsequently, in the 6th century, Greek philosophers provided documented evidence that the Earth is sphere through observation. They observed that the night sky looked different, as seen from various locations on Earth. Also, they have noted the Earth’s round shadow cast on the Moon during a lunar eclipse. Aside from that, these philosophers calculated the circumference of the Earth by measuring the shadow’s length of an object at exactly the same time, but on two different locations. Through this, they calculated that the Earth’s circumference was about 46,250 kilometers, making a close computation to the real value of 40,075 kilometers.
In 185, Chinese astronomers were first to document a supernova. Since then, numerous supernova explosions were observed, including the explosion in 1054, which was four times brighter than the planet Venus. Interestingly, some supernovae are bright enough to be seen during the day.
In the 16th century, Earth was commonly believed to be at the center of the solar system. This was known as the Geocentric model, where celestial bodies revolving around the Earth. However, this hypothesis did not match some observations, such as the movement of planets that appeared to move backward on their orbit. In 1543, a Polish astronomer named Nicolas Copernicus proposed a Heliocentric Model of the solar system in which the planets revolve around the Sun. This model described the unusual trajectory of the planets which the astronomers had observed. This new theory was one of the several revolutionary ideas in astronomy that appeared during the Renaissance period.
In the following years, astronomers Johaness Kepler and Tycho Brahe presented an accurate description of planetary movements, which led to the foundation of Isaac Newton’s theory of gravitation. Moreover, the previous observations were strengthened upon Galileo Galilei’s telescope’s invention in the 17th century. With the use of these telescopes, celestial objects like Jupiter’s four biggest moons were discovered. Over the centuries, astronomers around the world have formalized the observation of the sky by developing detailed catalogs of stars, star clusters, and nebulae. Following Uranus’ discovery in 1781, William Herschel opened new ideas in 1800 by discovering infrared radiation, a type of light that is not visible to the naked eye. During this discovery, others have benefited from the rapid advancement in the field of optics and imaging. Subsequently, in 1923, Edwin Hubble proved that the Andromeda Nebula extends beyond the Milky Way by using the 2.5 m-diameter, Hooker telescope.
In the second half of the 20th century, the advancements in the satellite launch enabled astronomers to collect information about the planets within the solar system. In addition, several space probes, including Venera, Mariner, and Voyager, were created and successfully ventured the space’s vastness.
Today, scientists are gathering data of celestial bodies using large telescopes both on the ground and in space. These modern telescopes, installed with massive mirrors, enable astronomers to catch the light of very faint and distant space objects. Also, these include specialized methods and advanced research tools developed to study the entire electromagnetic spectrum of light, radio waves, and x-rays. Modern large and complex telescopes, as well as advanced methods, have even made it possible for astronomers to directly observe phenomena such as distant exoplanets, black holes, and gravitational waves.