The word “Nebula” is derived from the Latin word meaning ‘cloud’. Nebulae are the basic building blocks of the universe. They are huge and diffused clouds of dust and gases such as helium, hydrogen formed by the gravitational collapse of gases in the interstellar medium. In the universe, they are seen as the most beautiful, colorful and glowing objects. Stars inside these nebulae (cloud) make them glow with the swirl of light. Most nebulae are composed of 10% hydrogens, 10% helium and 0.1% elements like carbon, nitrogen, calcium, magnesium, and iron.

There are different types of Nebulae.

Diffuse Nebulae- These nebulae are referred to as gaseous nebulae and have no distinct boundaries. They form massive stars as dust, gases and other materials clump together to form huge masses that are eventually ionized by UV radiations making it visible at optical wavelength. These stars are known as loose young clusters. They are divided into two- Emission Nebulae and Reflection Nebulae.

Emission nebulae contain high-temperature hydrogen gas within which the star energizes with UV radiation and glows in red color. The red color is due to loads of hydrogen. The Orion Nebula is an example of an emission nebula.

Reflection nebulae do not give way radiation of its own but reflect the light from nearby stars. The first diffuse nebula discovered was the Orion Nebula, M42. They are blue. The Trifid Nebula (M20) in the constellation of Sagittarius is an example of a reflection nebula.

Dark Nebulae- They are dark and dense clouds in front of distant stars or emission nebulae. The dark clouds appear because of interstellar dust particles coated with nitrogen and carbon monoxide and located in the dense and cold region of Giant Molecular Clouds. Small dark nebulae are called Bok globules. The largest dark nebulae visible to the naked eye are the Great Rift and the Coalsack Nebula.

Supernova Nebula- They are formed with the death of massive short-lived stars. This leads to an explosion and a blaze of glory. The explosion emits energy. The Crab Nebula in the constellation of Taurus is the best example of supernova nebula which was observed on July 4, 1054 AD by Arab and Chinese astronomers and labeled SN 1054. At the center of the nebula lies Neutron star.

Planetary Nebulae- Planetary Nebulae play a crucial role in the evolution of the galaxies. This is the ultimate stage of star-like Sun. When such stars come to age and had burned away all the hydrogen to helium in its core, its temperature increases and the star expands and evolves into red giants. They slowly lose their outer layers. The core remains as a hot central star that emits high energetic radiation. Helix Nebulae is the nearest planetary nebula.