1. Nebulae :
(From Latin: "cloud" pl. nebulae or nebulæ, with ligature or nebulas) is an interstellar cloud of dust, hydrogen gas, helium gas and other ionized gases. Nebulae are classified in four major groups :
H II regions, which encompass diffuse nebulae, bright nebulae, and reflection nebulae.
Planetary nebulae
Supernova remnant
Dark nebula
2.
Star clusters or star clouds :
Are groups of stars. Two types of star clusters can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars which are gravitationally bound, while open clusters, a more loosely clustered group of stars, generally contain less than a few hundred members, and are often very young.
3.
Galaxies:
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The name is from the Greek root galaxias [γαλαξίας], meaning "milky," a reference to the Milky Way galaxy. |
