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Astronomy refers to the study of the universe. It deals with the celestial objects such as planets, stars, comets, meteors, nebulae, and galaxies, and various phenomena involving these objects. It comes from two Greek words, "astro," which means "star," and "nomos," which means "law." Combining these two words, astronomy means "law of the stars."
Astronomy should not be confused with "astrology." The latter involves studying the stars and relating it to people's individual characteristics and to the future, which has no scientific basis compared to astronomy.
People were engaged in the practice of astronomy for thousands of years, making it one of the oldest sciences. In fact, people in ancient history frequently watched the stars and took note of their positions in space. Even before modern astronomy, they studied these clusters of stars called constellations.
At present, different equipment such as ground-based telescopes are now used in observing celestial objects in space. However, astronomers, who are scientists engaged in studying phenomena involving these celestial objects, use space probes and satellites to investigate the universe further.
In addition to these equipment used to observe the universe, astronomers also use equipment to determine the electromagnetic spectrum and radiation emitted in space. The use of these equipment particularly photometers and spectrometers enable discovery of celestial bodies, helping in increasing knowledge about the universe.
Astronomy has two main branches. Optical astronomy primarily uses telescopes to study visible objects in the universe, while non-optical astronomy deals with the study of characteristics in the universe that are not visible to the naked eye through the use of other sophisticated instruments aside from telescopes. One of these features is the electromagnetic spectrum, which gives us information on how the stars and other celestial bodies are formed.
There are numerous subfields in astronomy. Some of these are planetary astronomy, solar astronomy, stellar astronomy, galactic astronomy, extragalactic astronomy, and cosmology. Planetary astronomy, as the name implies, refers to the study of planets, as well as the comets and meteors, while stellar astronomy deals with the study of the stars and changes these stars undergo from creation to death. Although the sun is considered as a star, some references considered the study of the sun and its changes as a separate subfield, referring to it as solar astronomy.
Meanwhile, galactic astronomy is the study of the motion and evolution of the Milky Way galaxy, which eventually lead to the study of the formation of galaxies. On the other hand, extragalactic astronomy studies other galaxies in the universe outside the Milky Way to determine the extent of interaction among these galaxies.
Lastly, cosmology may sound differently compared to the other subfields in astronomy. It mainly seeks the answer to the question, "How does the universe look like before the Big Bang occurred?" It focuses on the creation of the universe.
Astronomy can also be divided according to its links with other branches of science. Astrobiology deals with the beginning and evolution of biological structures in the universe, while astrogeology answers the question, "What are the planets made of?" Astrophysics, conversely, refers to the study of the physical properties of the celestial bodies in the universe while astrochemistry studies the formation, distribution, and interaction of chemicals present in space.
So wide is the scope of astronomy that even its practice has its own branches. Professional astronomy is said to be divided into observational astronomy and theoretical astronomy. Observational astronomy refers to that branch that concentrates on getting data through observing celestial objects and analyzing them using the principles of physics. However, theoretical astronomy is said to be more focused on using computer or analytical models in studying these celestial objects and several phenomena in which these are involved.