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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.
Diffuse nebulae can be divided into emission nebulae, reflection nebulae and dark nebulae. Visible light nebulae may be divided into emission nebulae, which emit spectral line radiation from excited or ionized gas (mostly ionized hydrogen ); [ 25 ] they are often called H II regions , H II referring to ionized hydrogen), and reflection nebulae ...
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 .
NGC 7129 is a reflection nebula located 3,300 light years away in the constellation Cepheus. A young open cluster is responsible for illuminating the surrounding nebula. [2] A recent survey indicates the cluster contains more than 130 stars less than 1 million years old. [citation needed] NGC 7129 is located just half a degree from nearby ...
Based on the expansion rate, the estimated age of the nebula is 3,080 years. [5] The central star of the planetary nebula is a subdwarf O star with a spectral type of sdO. [7] The best fit model for this star gives an effective temperature of 100 kK, with 5,250 times the luminosity of the Sun [5] and 60.5% of the Sun's mass. [6]
IC 5146 (also Caldwell 19, Sh 2-125, Barnard 168, and the Cocoon Nebula) is a reflection [2] /emission [3] nebula and Caldwell object in the constellation Cygnus. The NGC description refers to IC 5146 as a cluster of 9.5 mag stars involved in a bright and dark nebula.
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Barnard 68 is a molecular cloud, dark absorption nebula or Bok globule, towards the southern constellation Ophiuchus and well within the Milky Way galaxy at a distance of about 125 parsecs (407 lightyears). [2] It is both close and dense enough that stars behind it cannot be seen from Earth.