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Reflection nebulae themselves do not emit significant amounts of visible light, but are near stars and reflect light from them. [25] Similar nebulae not illuminated by stars do not exhibit visible radiation, but may be detected as opaque clouds blocking light from luminous objects behind them; they are called dark nebulae. [25]
The closest and largest dark nebulae are visible to the naked eye, since they are the least obscured by stars in between Earth and the nebula, and because they have the largest angular size, appearing as dark patches against the brighter background of the Milky Way like the Coalsack Nebula and the Great Rift.
Planetary nebulae, represented here by the Ring Nebula, are examples of emission nebulae. An emission nebula is a nebula formed of ionized gases that emit light of various wavelengths. The most common source of ionization is high-energy ultraviolet photons emitted from a nearby hot star .
Reflection nebula are usually blue because the scattering is more efficient for blue light than red (this is the same scattering process that gives us blue skies and red sunsets). Reflection nebulae and emission nebulae are often seen together and are sometimes both referred to as diffuse nebulae. Some 500 reflection nebulae are known.
Planetary nebulae, which have nothing to do with planets despite the name, usually have a rounded structure and were so named because they initially resembled the disks from which planets form ...
A planetary nebula is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. [4] The term "planetary nebula" is a misnomer because they are unrelated to planets. The term originates from the planet-like round shape of these nebulae observed by astronomers through ...
The passage of a star ... You are looking at the Medusa Nebula ... a colorful cloudburst in deep space made up of particles and fragments from its dying star. Named after the mythological creature ...
The Orion Nebula is one of the most scrutinized and photographed objects in the night sky and is among the most intensely studied celestial features. [8] The nebula has revealed much about the process of how stars and planetary systems are formed from collapsing clouds of gas and dust.