<p>An arc spectrum is one produced by a discharge lamp where the discharge is through ionised gas, in the case of He-Ar a mixture of Helium and Argon, which produces a predictable line emission spectrum. </p>

<p>They are often used to provide a <a href="http://www.ing.iac.es/astronomy/observing/manuals/ps/tech_notes/tn070_1.pdf">calibration spectrum for spectrometers</a>.</p>

CC BY-SA 3.0
2015-12-05T05:56:03.497Z
An electric arc, in air, between two *iron* electrodes, is also used as a source of reference emission lines...
DJohnM
CC BY-SA 3.0
2015-12-01T16:01:14.043Z
2015-12-01T16:01:14.043Z
Conrad Turner
<p>I sometimes hear about astronomers using an arc spectrum to calibrate observations. For example a "He-Ar arc spectrum". What is an "arc" in this context? I assume it's nothing got to do with angles (arcmin, arcsec, etc.). </p>

CC BY-SA 3.0
2015-12-01T14:53:45.290Z
@ConradTurner, you could add some more details and make an answer out of your comment !
Py-ser
CC BY-SA 3.0
2015-12-02T08:24:09.763Z
@LocalFluff See Conrad's answer. The arc refers to a discharge lamp.
ProfRob
<observational-astronomy><amateur-observing><spectroscopy><spectra>
What is an "arc" spectrum ?
Realta
# What is an "arc" spectrum ?

(Asked by: username_0 on 2015-12-01)

I sometimes hear about astronomers using an arc spectrum to calibrate observations. For example a "He-Ar arc spectrum". What is an "arc" in this context? I assume it's nothing got to do with angles (arcmin, arcsec, etc.).

**Tags:** observational-astronomy, amateur-observing, spectroscopy, spectra

> **Comments:**
> **username_1**: @ConradTurner, you could add some more details and make an answer out of your comment !  
> **username_2**: @LocalFluff See Conrad's answer. The arc refers to a discharge lamp.  

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## 1 answers

### Answer by username_3 on 2015-12-01. Score: 6

An arc spectrum is one produced by a discharge lamp where the discharge is through ionised gas, in the case of He-Ar a mixture of Helium and Argon, which produces a predictable line emission spectrum.

They are often used to provide a [calibration spectrum for spectrometers](http://www.ing.iac.es/astronomy/observing/manuals/ps/tech_notes/tn070_1.pdf).

> **Comments:**
> **username_4**: An electric arc, in air, between two *iron* electrodes, is also used as a source of reference emission lines...  

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