Galaxy is a noun that refers to a vast system of stars, gas, dust, and other celestial objects bound together by gravity. It constitutes a fundamental building block of the universe, forming structures on scales ranging from a few million to several billion light-years across.
A galaxy typically contains billions to trillions of stars, along with countless planets, asteroids, comets, and interstellar matter. These celestial entities rotate around a central region called the galactic core or nucleus. Within a galaxy, stars cluster together forming various shapes such as spirals, ellipticals, and irregulars.
The galaxy we inhabit is known as the Milky Way, a barred spiral galaxy with a diameter of about 100,000 light-years. It is composed of a multitude of stars, including our sun, and hosts numerous planetary systems. Galaxies come in diverse sizes and forms, exhibiting remarkable variations in structure, mass, composition, and activity.
The concept of galaxy originated from the Greek word "galaxias," meaning "milky," which was used to describe the hazy band of light observed across the night sky caused by numerous stars. The study of galaxies, known as galactic astronomy, encompasses research on their formation, evolution, composition, interactions, and other fundamental aspects, contributing to our understanding of the universe's nature and history.
