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

 There are different types of Nebulae.

Diffuse Nebulae- These nebulae are referred to gaseous nebulae and  have no distinct boundaries. They form massive stars as dust, gases and other materials clump together to form huge masses which are eventually ionised by UV radiations making it visible at optical wavelength. These star 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 the loads of hydrogen. The Orion Nebula is an example of emission nebula.

 Reflection nebulae do not give way radiation of its own but reflects the light from nearby stars. The first diffuse nebula discovered was the Orion Nebula, M42. They are blue in color. The Trifid Nebula (M20) in 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 a massive short-lived stars. This leads to  explosion and a blaze of glory. The explosion emits energy. The Crab Nebula in constellation of Taurus is the best example of supernova nebula which was observed on July 4, 1054 AD by Arab and Chinese astronomers and labelled 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 comes to age and had burned away all the  hydrogen to helium in its core, its temperature increases and the star expands and evolve into red giants.They slowly lose their outer layers. The core remains as hot central star which emits high energetic radiation. Helix Nebulae is the nearest planetary nebula.