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Clara Chung
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Why can't hydrogen gas on the stars be detected by using line emission spectrum of hydrogen. Why must we use line absorption spectrum to detect?
That was a question I asked , myself once. The light is absorbed from the direction of the source and then re-emitted in all directions so what you see is a dim line at the absorbed frequency.Drakkith said:As a follow on question to the OP's, why do we see an absorption line at all? Why doesn't the hydrogen (and other elements) simply re-emit the same light a short time later, resulting in a continuous spectrum?
sophiecentaur said:That was a question I asked , myself once. The light is absorbed from the direction of the source and then re-emitted in all directions so what you see is a dim line at the absorbed frequency.
Emission and absorption lines
When heated every element gives off light. When this light is decomposed using a prism it is found to be made up of a series of ``lines'', that is, the output from the prism is not a smooth spectrum of colours, but only a few of them show up. This set of colours is unique to each element and provides a unique fingerprint: if you know the colour lines which make up a beam of light (and you find this out using a prism), you can determine which elements were heated up in order to produce this light.
Similarly, when you shine white light through a cold gas of a given element, the gas blocks some colours; when the ``filtered'' light is decomposed using a prism the spectrum is not full but shows a series of black lines (corresponding to the colours blocked by the gas); see Fig. 8.3. For a given element the colours blocked when cold are exactly the same as the ones emitted when hot.
The Fraunhofer lines are typical spectral absorption lines. Absorption lines are dark lines, narrow regions of decreased intensity, that are the result of photons being absorbed as light passes from the source to the detector. In the Sun, Fraunhofer lines are a result of gas in the photosphere, the outer region of the sun. The photosphere gas is colder than the inner regions and absorbs light emitted from those regions.
The energy has to be re-emitted after a finite (short) time. It can't be stored up.davenn said:not re-emission
sophiecentaur said:The energy has to be re-emitted after a finite (short) time. It can't be stored up.
I don't see how you can say that. Photons are absorbed (light on the path from the star to you) and they are then re-emitted in all directions, so each gas atom is a point source, from which you (in one particular direction) get onlydavenn said:yes, but it isn't the cause of the dark absorption line
A line absorption spectrum is a pattern of dark lines seen in a continuous spectrum of light, created when light from a hot, dense source passes through a cooler, less dense gas. The gas absorbs specific wavelengths of light, leaving behind dark lines in the spectrum.
By analyzing the dark lines in a star's spectrum, scientists can determine the elements present in the star's atmosphere. Each element has a unique pattern of absorption lines, allowing scientists to identify the composition of a star. The spectrum can also reveal information about a star's temperature, density, and motion.
The dark lines in a line absorption spectrum are caused by the absorption of specific wavelengths of light by the elements present in a star's atmosphere. When light from the star passes through the cooler, less dense gas, the gas absorbs certain wavelengths of light, leaving behind dark lines in the spectrum.
The line absorption spectrum and emission spectrum are two types of spectra that result from the interaction of light and matter. The line absorption spectrum is created when light from a hot, dense source passes through a cooler, less dense gas, while the emission spectrum is created when a hot, dense gas emits light. The line absorption spectrum has dark lines, while the emission spectrum has bright lines.
Yes, the line absorption spectrum can provide information about the age of a star. As stars age, their chemical composition changes, and the absorption lines in their spectra shift. By analyzing the pattern and position of these lines, scientists can estimate the age of a star.