<p>The key thing about lines is that they have a higher opacity than the continuum, so they are generally formed in layers that are above where the continuum formed.  Thus there are two general ways to get emission lines (i.e., lines that are brighter than the continuum), one is to make the higher regions hotter than what is below, and the other is to make them physically larger.  The first means that at line wavelengths, the object looks brighter, and the second means that at line wavelengths, the object looks larger.  The first happens in what is called a "chromosphere" of the star (a shell that is hotter because of some additional heating going on above the photosphere of the star), and the second happens if the star has a wind or anything else that physically extends it in ways that are transparent in the continuum but can be seen in lines.</p>

<p>The third way to get emission lines is if the continuum is not optically thick (i.e., the object is transparent in the continuum), as happens with various low-density nebulae, but your question seems to stipulate that there is a bright continuum there, so there is an opaque object emitting something akin to blackbody radiation.  </p>

CC BY-SA 3.0
2017-01-02T16:54:56.263Z
And perhaps it should be added that you can get emission lines a fourth way, by stimulated emission as mentioned in the question, but this is quite rare as it requires a "population inversion" like you need in lasers.  When this does happen, which is not often, it can happen in the microwave regime, so you will hear of astrophysical "masers," but few emission lines are formed that way.
Ken G
CC BY-SA 3.0
2017-01-02T14:06:25.113Z
2017-01-02T14:06:25.113Z
Ken G
<p>Ionised gas will emit radiation at particular frequencies, Nebulae that generate their own light this way are called "Emission nebulae" and they have spectra that are characterised by a collection of bright lines. They contrast with reflection nebulae that are lit by bright stars.</p>

<p>Stars also have part of their spectrum that exceeds what would be expected from a blackbody due to emission from gas in their photosphere's </p>

CC BY-SA 3.0
2017-01-02T11:07:03.673Z
2017-01-02T11:07:03.673Z
James K
<p>Dark lines in a continuum spectrum is common. But are there bright lines too? </p>

<p>By the stimulated emission process, the light can also be amplified, right?</p>

<p>In this case, we should get bright lines instead of dark lines.</p>

CC BY-SA 3.0
2016-02-11T14:36:14.050Z
Can you provide a bit more context? Half of astronomy is based on the existence of emission lines, both from stimulated emission, but also from other types of emission processes, like recombination and collisions. Is this what you mean?
pela
CC BY-SA 3.0
2016-02-12T14:12:17.287Z
yes : http://stars.astro.illinois.edu/sow/spectra.html#nebulae
James K
CC BY-SA 3.0
2016-04-15T00:00:20.143Z
The dark lines on the emission spectrum of the sun are called Fraunhofer lines. https://en.wikipedia.org/wiki/Fraunhofer_lines
MaxW
<spectroscopy>
Bright lines in a continuum spectrum
John
# Bright lines in a continuum spectrum

(Asked by: username_0 on 2016-02-11)

Dark lines in a continuum spectrum is common. But are there bright lines too?

By the stimulated emission process, the light can also be amplified, right?

In this case, we should get bright lines instead of dark lines.

**Tags:** spectroscopy
> **Comments:**
> **username_1**: Can you provide a bit more context? Half of astronomy is based on the existence of emission lines, both from stimulated emission, but also from other types of emission processes, like recombination and collisions. Is this what you mean?  
> **username_2**: yes : http://stars.astro.illinois.edu/sow/spectra.html#nebulae  
> **username_3**: The dark lines on the emission spectrum of the sun are called Fraunhofer lines. https://en.wikipedia.org/wiki/Fraunhofer_lines  

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## 2 answers

### Answer by username_4 on 2017-01-02. Score: 3

The key thing about lines is that they have a higher opacity than the continuum, so they are generally formed in layers that are above where the continuum formed. Thus there are two general ways to get emission lines (i.e., lines that are brighter than the continuum), one is to make the higher regions hotter than what is below, and the other is to make them physically larger. The first means that at line wavelengths, the object looks brighter, and the second means that at line wavelengths, the object looks larger. The first happens in what is called a "chromosphere" of the star (a shell that is hotter because of some additional heating going on above the photosphere of the star), and the second happens if the star has a wind or anything else that physically extends it in ways that are transparent in the continuum but can be seen in lines.

The third way to get emission lines is if the continuum is not optically thick (i.e., the object is transparent in the continuum), as happens with various low-density nebulae, but your question seems to stipulate that there is a bright continuum there, so there is an opaque object emitting something akin to blackbody radiation.

> **Comments:**
> **username_4**: And perhaps it should be added that you can get emission lines a fourth way, by stimulated emission as mentioned in the question, but this is quite rare as it requires a "population inversion" like you need in lasers.  When this does happen, which is not often, it can happen in the microwave regime, so you will hear of astrophysical "masers," but few emission lines are formed that way.  

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### Answer by username_2 on 2017-01-02. Score: 1

Ionised gas will emit radiation at particular frequencies, Nebulae that generate their own light this way are called "Emission nebulae" and they have spectra that are characterised by a collection of bright lines. They contrast with reflection nebulae that are lit by bright stars.

Stars also have part of their spectrum that exceeds what would be expected from a blackbody due to emission from gas in their photosphere's


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