nebula (nĕb`y
lə) [Lat.,=mist], in astronomy, observed manifestation of a collection of highly rarefied gas and dust in interstellar space. Prior to the 1960s this term was also applied to bodies later discovered to be galaxies galaxy, large aggregation of stars , gas, and dust, typically containing billions of stars. Recognition that galaxies are independent star systems outside the Milky Way came from a study of the Andromeda Galaxy (1926–29) by Edwin P.
..... Click the link for more information. , e.g., the so-called Great Nebula in the constellation Andromeda. In 1864, William Huggins confirmed William Herschel's conclusion that nebulae are not swarms of stars by determining that the spectra of nebulae are made of bright lines characteristic of radiating gases. Diffuse nebulae and planetary nebulae are two major classifications of these objects. Diffuse nebulae appear as light or dark clouds (called bright and dark nebulae), are irregular in shape, and range up to 100 light-years in diameter. Some bright nebulae, composed primarily of hydrogen gas ionized by nearby hot blue-white stars, radiate their own light; they are called emission nebulae and are characterized by narrow spectral emission lines. Other bright nebulae, existing near cooler stars and not receiving the radiation necessary to make them self-luminous, reflect the starlight and are called reflection nebulae. Over 300 bright nebulae have been cataloged; prime examples are the Orion Nebula Orion Nebula, bright diffuse nebula in the constellation Orion; also known as the Great Nebula of Orion and cataloged as M42 or NGC 1976. It is located near the middle of the "sword" hanging from Orion's "belt" of stars.
..... Click the link for more information. , visible to the unaided eye, the Eta Carinae Nebula, and the smaller North America Nebula. Dark nebulae are detected as empty patches in a field of stars or as dark clouds obscuring part of a bright nebula in the background, as in the case of the Horsehead Nebula. Smaller bodies of dark nebulous matter having unusually high densities have been observed in some bright nebulous regions. Many astronomers believe that these bodies, called globules, are in the process of condensation and are the initial stages in the birth of stars. Planetary nebulae appear through the telescope as small disks with well-defined boundaries. They are the last stage of evolution for most stars, including the sun. Each consists of a shell of gaseous material surrounding a central hot star that emits radiation causing this material to glow. These shells measure about 20,000 AU in diameter (1 AU is the mean distance between the earth and the sun) and are slowly expanding, which suggests that they were expelled by the stars in nova eruptions.
nebula
nebula [′neb·yə·lə]
lə) [Lat.,=mist], in astronomy, observed manifestation of a collection of highly rarefied gas and dust in interstellar space. Prior to the 1960s this term was also applied to bodies later discovered to be galaxies galaxy, large aggregation of stars , gas, and dust, typically containing billions of stars. Recognition that galaxies are independent star systems outside the Milky Way came from a study of the Andromeda Galaxy (1926–29) by Edwin P...... Click the link for more information. , e.g., the so-called Great Nebula in the constellation Andromeda. In 1864, William Huggins confirmed William Herschel's conclusion that nebulae are not swarms of stars by determining that the spectra of nebulae are made of bright lines characteristic of radiating gases. Diffuse nebulae and planetary nebulae are two major classifications of these objects. Diffuse nebulae appear as light or dark clouds (called bright and dark nebulae), are irregular in shape, and range up to 100 light-years in diameter. Some bright nebulae, composed primarily of hydrogen gas ionized by nearby hot blue-white stars, radiate their own light; they are called emission nebulae and are characterized by narrow spectral emission lines. Other bright nebulae, existing near cooler stars and not receiving the radiation necessary to make them self-luminous, reflect the starlight and are called reflection nebulae. Over 300 bright nebulae have been cataloged; prime examples are the Orion Nebula Orion Nebula, bright diffuse nebula in the constellation Orion; also known as the Great Nebula of Orion and cataloged as M42 or NGC 1976. It is located near the middle of the "sword" hanging from Orion's "belt" of stars.
..... Click the link for more information. , visible to the unaided eye, the Eta Carinae Nebula, and the smaller North America Nebula. Dark nebulae are detected as empty patches in a field of stars or as dark clouds obscuring part of a bright nebula in the background, as in the case of the Horsehead Nebula. Smaller bodies of dark nebulous matter having unusually high densities have been observed in some bright nebulous regions. Many astronomers believe that these bodies, called globules, are in the process of condensation and are the initial stages in the birth of stars. Planetary nebulae appear through the telescope as small disks with well-defined boundaries. They are the last stage of evolution for most stars, including the sun. Each consists of a shell of gaseous material surrounding a central hot star that emits radiation causing this material to glow. These shells measure about 20,000 AU in diameter (1 AU is the mean distance between the earth and the sun) and are slowly expanding, which suggests that they were expelled by the stars in nova eruptions.
Bibliography
See L. Allen, Atoms, Stars, and Nebulae, (3d ed. 1991).
nebula
Any of various tenuous clouds of gas and dust in interstellar space. Nebulae constitute only a small percentage of a galaxy's mass. Dark nebulae (e.g., the Coalsack) are very dense, cold molecular clouds that appear as large, obscure, irregularly shaped areas in the sky. Bright nebulae (e.g., the Crab Nebula, planetary nebula) appear as faintly luminous, glowing surfaces; they emit their own light or reflect that of stars near them. The term nebula also formerly referred to galaxies outside the Milky Way Galaxy.
nebula
1. Astronomy a diffuse cloud of particles and gases (mainly hydrogen) that is visible either as a hazy patch of light (either an emission or a reflection nebula) or an irregular dark region against a brighter background (dark nebula)
2. Pathol
a. opacity of the cornea
b. cloudiness of the urine
3. any substance for use in an atomizer spray
nebula [′neb·yə·lə]
(astronomy)
Interstellar clouds of gas or small particles; an example is the Horsehead Nebula in Orion.
| Nebula - An early business-oriented language from ICL for the
Ferranti Orion computer. ["NEBULA - A Programming Language for Data Processing", T.G. Braunholtz et al, Computer J 4(3):197-201 (1961)]. |
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