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Topic: Stellar atmosphere

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  stellar | English | Dictionary & Translation by Babylon
Stellar*, a New Zealand-based rock bandStellar aberration is an astronomical phenomenon defined as an apparent motion of the heavenly bodies due to a combination of the motion of the Earth and the finite velocity of light.A stellar association is a very loose star cluster, looser than both open clusters and globular clusters.
Stellar astronomy is the study of stars and the phenomena exhibited by the various forms/developmental stages of stars.
Stellar dynamics is the branch of astrophysics which describes in a statistical way the collective motions of stars subject to their mutual gravity.A stellar engine is a hypothetical propulsion device that employs a significant part of a star's radiation to change the star's velocity (literally: an engine for a star).
www.babylon.com /definition/stellar   (556 words)

  Stellar atmosphere -- Facts, Info, and Encyclopedia article   (Site not responding. Last check: 2007-11-04)
All stars possess a so-called (The intensely luminous surface of a star (especially the sun)) photosphere, which is the lowest and coolest part of the star's atmosphere - and as the photosphere is the part which we see with our eyes (hence the name) you can think of it as the surface of the star.
Above the photosphere, which ranges in temperature from around 3000 degrees to about 10 times as much, comes the (A gaseous layer of the sun's atmosphere (extending from the photosphere to the corona) that is visible during a total eclipse of the sun) chromosphere.
An unresolved problem in stellar (The branch of astronomy concerned with the physical and chemical properties of celestial bodies) astrophysics is the question as to how exactly the corona can be heated to such high temperatures.
www.absoluteastronomy.com /encyclopedia/s/st/stellar_atmosphere.htm   (392 words)

 Stellar atmosphere - Wikipedia, the free encyclopedia
All stars possess a so-called photosphere, which is the lowest and coolest part of the star's atmosphere - and as the photosphere is the part which we see with our eyes (hence the name) you can think of it as the surface of the star.
This part of the atmosphere first cools down and then starts to heat up to about 10 times the temperature of the photosphere.
An unresolved problem in stellar astrophysics is the question as to how exactly the corona can be heated to such high temperatures.
en.wikipedia.org /wiki/Stellar_atmosphere   (274 words)

 Modeling Nonstandard Stellar Atmospheres   (Site not responding. Last check: 2007-11-04)
Stellar astronomers have a more difficult time determining the location for a particular star on the H-R diagram because the interpretation of the observable spectrum depends largely on theories about the ways that spectrum is produced in the atmosphere of a star.
Models of stellar atmospheres are then key to the correct disposition of stars on the H-R diagram, meaning that the interpretation of the life histories of stars--both individually and collectively--depends on stellar atmosphere models.
Standard stellar atmosphere models are based in large part on what has been learned from the nearest star, the Sun; therefore, the masses of stars are usually expressed in terms of the solar mass, taken as 1.
www.sdsc.edu /GatherScatter/GSfall95/3stellar.html   (1051 words)

 stellar - Search Results - MSN Encarta
Stellar Parallax, apparent change in star position, used in determining stellar distances.
The only visible part of a star is its gaseous outer region, or atmosphere.
The atmosphere of the Sun is about 320 km (about 200 mi) thick, while the...
encarta.msn.com /stellar.html   (143 words)

 Stellar Structure and Evolution
One of the triumphs of stellar evolution theory is a detailed understanding of the preferred location of stars in the physical Hertzsprung-Russell diagram, which plots luminosity versus temperature (Figure 17).
A stellar model is constructed by solving the four basic equations of stellar structure: (1) conservation of mass; (2) conservation of energy; (3) hydrostatic equilibrium and (4) energy transport via radiation, convection and/or conduction.
Given a stellar structure model, the oscilation frequencies are then predicted, and compared with the measurements, thus testing the underlying physics of the assumed stellar structure.
www.rssd.esa.int /SA-general/Projects/GAIA_files/LATEX2HTML/node64.html   (1076 words)

 ESO - 2002
A stellar occultation provides a useful opportunity to study the planetary atmosphere, by means of accurate photometric measurements of the dimming of the stellar light, as the planet moves in front of the star.
Pluto's atmosphere was first detected on August 19, 1985, during a stellar occultation observed from Israel and then studied in more detail from Australia and from the Kuiper Airborne Observatory (KAO) during another such event on July 9, 1988.
The present observations aimed at discriminating between the current theoretical models of Pluto's atmosphere by means of detailed measurements of the changing intensity and colour of the stellar light, as the star is seen through progressively lower layers of the planet's atmosphere.
www.eso.org /outreach/press-rel/pr-2002/phot-21-02.html   (1711 words)

 SAE01as   (Site not responding. Last check: 2007-11-04)
We will define a star's atmosphere as the region where the transport of radiant energy shifts from diffusion (that is, the mean free path of photons is much shorter than the scale lengths of the variations of physical quantities such as temperature and pressure) to the free streaming of radiation into fl space.
The whole grand story of stellar evolution and nucleosynthesis, from giant molecular clouds to supernova remnants, rests on the interpretation of observations based on the pioneering studies of radiative transfer and equilibrium performed by Sir Arthur Eddington and others in the early part of this century.
Therefore, the student of atmospheric physics must first understand the background spectrum produced by a star, and then understand the signatures of his or her particular interest imprinted on this spectrum.
www.physics.utoledo.edu /~lsa/_atmos/SAE01as.htm   (1690 words)

 Stellar Occultations Reveal Drastic Expansion Of Pluto's Atmosphere
With an atmosphere, however, there will be a gradual dimming of the starlight, as the stellar rays are increasingly refracted when traversing thicker and thicker amounts of gas, see the movie at the end.
One might naively expect an overall collapse of the atmosphere: the gases should freeze onto the surface as the planet moves farther from the Sun and cools.
The spikes are caused by small atmospheric temperature and density fluctuations, maintained either by strong winds between the lit and dark hemisphere of the planet, or by convection near the surface of Pluto.
www.spacedaily.com /reports/Stellar_Occultations_Reveal_Drastic_Expansion_Of_Plutos_Atmosphere.html   (1284 words)

 AllRefer.com - stellar structure (Astronomy, General) - Encyclopedia
stellar structure, physical properties of a star and the processes taking place within it.
Except for that of the sun, astronomers must draw their conclusions regarding stellar structure on the basis of light and other radiation from stars that are light-years away; this light enables them to observe only the stars' surfaces.
Such a spectrum consists of a continuous fl body spectrum produced by complex conditions within the star superimposed on which is a series of dark lines due to absorption of energy by the cooler stellar atmosphere.
reference.allrefer.com /encyclopedia/S/stellars.html   (501 words)

 ipedia.com: Celestial body atmosphere Article   (Site not responding. Last check: 2007-11-04)
Atmosphere is the general name for a layer of gases that may surround a material body of sufficient mass.
Atmospheric gases are lost to space when the individual molecules' thermal motion exceeds the escape velocity of the body.
Other mechanisms that can cause atmosphere depletion are solar wind-induced sputtering, impact erosion, weathering, and sequestration—sometimes referred to as "freezing out"—into the regolith and polar caps.
www.ipedia.com /celestial_body_atmosphere.html   (280 words)

 NAI - Astronomy Focus Group - Transit of Venus   (Site not responding. Last check: 2007-11-04)
ApJ 2002) relies on the assumption that the integrated stellar spectrum is the same in transit and out of transit, and that the integrated stellar spectrum is the same during different stages of the transit.
The integrated stellar spectrum is altered during a planet transit due to stellar rotation.
The integrated stellar spectrum is altered by a transiting planet due to the fact that spectral lines form at different depths in the stellar atmosphere (e.g., the line core vs. the line wings).
www.dtm.ciw.edu /seager/NAIAFG/AFGVenusFAQ.html   (1391 words)

 [No title]   (Site not responding. Last check: 2007-11-04)
in a stellar atmosphere, gaseous nebula or in a terrestrial laboratory - through the analysis of its spectrum.
At such temperatures the stellar atmosphere is mostly ionized and the energy transport through the atmosphere is purely radiative.
Based on this and additional information on the distances to the stars, the fundamental stellar parameters -- mass, luminosity, radius, chemical composition -- are also determined with high precision.
www.sternwarte.uni-erlangen.de /~ai32/research_qs.html   (466 words)

 The Classification of Stellar Spectra
Stellar spectra with absorption line spectra characteristic of elements in the stellar atmospheres.
Thus, stellar peculiarities are indicated in the form of lowercase letter added to the end of a spectral type.
This may explain stellar types which have cooler surface temperatures (<3200 K) than M stars but have spectral features as if their outer atmospheres had been enriched with heavier elements.
faculty.pepperdine.edu /dgreen/Astronomy/Resources/StellarClass/classification_of_stars.htm   (1407 words)

 Star (astronomy) - MSN Encarta
Astronomers can infer many of the properties of the star’s interior by studying the star’s atmosphere, its size, and the energy the star releases.
The atmosphere of the Sun is about 320 km (about 200 mi) thick, while the Sun’s diameter is 1,392,000 km (865,000 mi).
Even though the atmosphere is relatively small compared to the size of the entire star, astronomers can learn a great deal about a star by studying its atmosphere.
encarta.msn.com /encyclopedia_761557483/Star_(astronomy).html   (1042 words)

 [No title]
At the time of this writing a new set of stellar atmospheres is being computed, and until it is ready you will need to use the "first generation" H-Ca set.
Some of the stellar atmosphere files are very large, and reading them using sequential access would be very slow.
Often only one or two of the sets of stellar atmospheres are needed, not the whole lot.
www.nublado.org /Cloudy_old/c94/c94_stars.htm   (901 words)

 Imaging the Surfaces of Stars
The SKA will be able to image the structure and directly measure the temperature of these stellar atmospheres over a relatively large range of heights, leading to more accurate empirical models of their physical properties as well as a better understanding of the mechanisms that drive the stellar atmosphere outwards.
Thus, study of the properties and dynamics of the stellar atmosphere leading to a better understanding of the mechanisms responsible for their large extents and mass outflows is one of the important topics in red giant and supergiant star research.
Comparisons of the atmospheric structure at different heights will be vital for understanding both the physical properties and dynamics of the stellar atmosphere, and (combined with optical photospheric images) will provide powerful constraints on the mechanisms responsible for driving the atmosphere outwards.
www.ras.ucalgary.ca /SKA/science/node14.html   (2290 words)

 Top Story - HOT, YOUNG STARS COOL DOWN A BIT - June 03, 2002
The result was obtained by comparing a sophisticated new model of stellar atmospheres to recent observations of young, massive stars in the Small Magellanic Cloud, a nearby galaxy.
The new stellar atmosphere model estimates how light from O stars would appear as it passes through their atmospheres on the way to Earth.
The researchers compared spectra from their observations to various predicted spectra derived from the new stellar atmosphere model, and discovered that the best matches were to ones based on cooler temperatures.
www.gsfc.nasa.gov /topstory/20020603startemp.html   (1490 words)

 Radiative shocks in stellar atmospheres   (Site not responding. Last check: 2007-11-04)
The temperature of the stellar ``surface'' is typically between 3000K and 20,000K depending on the star.
The atmosphere is relatively large, between 10 and 100% of the stellar radius i.e., a few million kilometers.
In the stellar interior the amplitude of oscillations rapidly decreases to the center of the star.
www.obs-hp.fr /www/preprints/pp127/node1.html   (665 words)

 High Energy Astrophysics Picture Of the Week
But stellar magnetic fields are much more complex than the earth's magnetic field, since the hot ionized gas in a stellar interior moves in complicated flows and streams, producing localized strong magnetic fields.
Stellar magnetic activity produces the stellar corona, a region of extremely hot gas (temperatures exceeding one million degrees) in the outer stellar atmosphere, and generates other observable phenomena like sunspots and stellar flares.
One useful means of studying stellar activity is to study the X-ray emission produced by the hot stellar corona.
heasarc.gsfc.nasa.gov /docs/objects/heapow/archive/stars/44iboo_chandra.html   (398 words)

 IAAT (Astronomy): Stellar Atmospheres Group - Research Activities
The general context of this work is the stellar evolution, especially the late stages of intermediate mass stars which end their life as white dwarfs.
This requires high quality spectra from ground and space based observatories covering the stellar spectrum form X-rays to the infrared (see also Section Observation) as well as sophisticated computer simulations (see Section Theory) of the interaction between the radiation field with the hot plasma in the outer layers of the star.
Stellar spectra are obtained at ground or space based observatories described in the next section, the calculation of synthetic spectra are shortly described here.
astro.uni-tuebingen.de /groups/stellar   (1122 words)

 Carbon stars
As the atmosphere of these stars is enriched by convection from the elements synthetized in their core, this mass loss enriches the interstellar medium of the Galaxy in heavy elements, carbon in particular, and dust.
In this case the carbon enrichment is thought to be due to the dredge-up of carbon, recently synthesized in the stellar core, to the stellar surface by convection.
Under the action of this pulsation the atmosphere is extended and, in the upper layers, the matter may reach a temperature low enough for some elements to condense into very small particles ("star dust").
www.obspm.fr /actual/nouvelle/jul03/irts.en.shtml   (973 words)

 Stellar Atmospheres Software
In order to interpret stellar spectra, it is necessary to construct models which accurately represent the structure of a stellar atmosphere and the transfer of radiation from the stellar interior into interstellar space.
For the study of helium stars and other stellar remnants, we in Armagh use several computer programs, of which sterne and spectrum are the most important.
Opacity in the stellar atmosphere modifies the emergent energy distribution, so that it in order to solve for the above quantities it is necessary to compare theoretical models of stellar energy distributions with that observed.
star.arm.ac.uk /~csj/software_store   (1211 words)

 Stellar atmospheres group - Uppsala
The understanding of stellar atmospheres, i.e., the layers of the stars that can be directly observed, is still not satisfactory.
The ambition of the Stellar Atmospheres Group is to contribute to the basic physical understanding of stellar atmospheres and, by application of model atmospheres of late-type stars, to the study of stellar and galactic evolution and cosmology.
In recent years, the scope of the stellar atmospheres group has broadened, not only towards galactic studies but also towards problems related to stellar structure and evolution.
www.astro.uu.se /atmos   (186 words)

 Mira Behind The Molecules
This model is the first ever to explain the structure of Mira stars over a wide range of spectral wavelengths from the visible to the mid-infrared and to be consistent with the theoretical properties of their pulsation.
The carbon, nitrogen, oxygen and other elements of which we are made were mostly produced in the interior of such stars (with heavier elements coming from supernovae), and are then returned to space via this mass loss to become part of new stars and planets.
The maturing technique of interferometry is revealing details of the Mira atmosphere, bringing scientists close to observing and understanding the production and ejection of molecules and dust, as these stars recyle their contents on an astronomical scale.
www.spacedaily.com /news/stellar-04q.html   (1100 words)

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