<p><a href="https://i.sstatic.net/Mtj2Y.png" rel="noreferrer"><img src="https://i.sstatic.net/Mtj2Y.png" alt="SDSS Plug Plate" /></a></p>
<p>I imagine it's done differently based on the goals.  Anything wanting to study just one object could simply mask out everything else.  But the <a href="https://www.sdss.org/" rel="noreferrer">Sloan Digital Sky Survey</a> studies numerous objects at once.  The method they use is to create a &quot;plug plate&quot; corresponding to each object to be studied.  A fiber optic cable was attached to each hole and ran to a separate spectrograph to study that object.</p>
<p>The article <a href="https://voyages.sdss.org/preflight/sdss-plates/" rel="noreferrer">SDSS Plates</a> has more information, including a video on the making of the plates, and another showing the fiber optic hookups.</p>
<p>The image above is the bare plate, and the image below is the plate with the cables hooked up.</p>
<p><a href="https://i.sstatic.net/gvjc6.jpg" rel="noreferrer"><img src="https://i.sstatic.net/gvjc6.jpg" alt="SDSS Plug Plate with cables" /></a></p>

CC BY-SA 4.0
2022-11-12T02:58:29.697Z
This is very helpful but on a satellite I don't think a plug plate is used because the satellite keeps moving and the orientation of the objects changes. Are there any other ways to find the spectra?
Aakarsh Tathachar
CC BY-SA 4.0
2022-11-12T17:54:44.853Z
Telescopes on the ground are also moving, even more so than those in Earth orbit.  A satellite's motion around the Earth will be negligible as long as it maintains its orientation.  But they won't have people there to switch out the plates.  So, as I said above, they're more likely to just mask off everything but one object using an adjustable mask.
Greg Miller
CC BY-SA 4.0
2022-11-12T22:44:12.317Z
More about fiber arrays: [How exactly will DESI simultaneously capture individual spectra from 5,000 galaxies using optical fibers?](https://astronomy.stackexchange.com/q/33804/7982) and [What is the dimensions of the smallest object detectable by an optical fiber from a specific distance?](https://astronomy.stackexchange.com/q/29111/7982)
uhoh
CC BY-SA 4.0
2022-11-12T22:44:53.263Z
Can you support the idea that fibers can be used to capture just one object by adding some quantitative information? This is certainly multimode fiber with a core diameter of at least tens of microns if not hundreds; can you find an actual number and translate to arcseconds? Also, does the far end of the fiber feed the spectrometer directly or is there still a narrow slit at each fiber's output?
uhoh
CC BY-SA 4.0
2022-11-12T22:48:31.140Z
@AakarshTathachar The big space telescopes do have some amazing guidance systems to keep themselves pointing in the same direction during measurements with very high stability, but there might be other reasons why an optical fiber-based spectrometers are unsuitable for space telescopes. I think you can ask a new question "Have optical fibers ever been used to collect and transfer light in space telescopes?" and you can link back here for background.
uhoh
CC BY-SA 4.0
2022-11-12T23:05:38.080Z
That is good for more understanding but I was just wondering if this system can identify the main concentration of fire in a forest fire under a cover of trees and smoke. If this technique isn't used, would it be more efficient?
Aakarsh Tathachar
CC BY-SA 4.0
2022-11-12T23:11:27.070Z
@uhoh As mentioned in the first link ProfRob provided, the individual fibers have diameters of 3 arc seconds in the case of the original spectrograph and 2 arc seconds for the newer (“BOSS”) spectrograph.
Peter Erwin
CC BY-SA 4.0
2022-11-12T23:20:03.057Z
@uhoh I’m sorry, I meant Greg Miller’s answer!
Peter Erwin
CC BY-SA 4.0
2022-11-12T23:22:17.367Z
@PeterErwin okay great! That will be very helpful if moved back into the answer post itself.
uhoh
CC BY-SA 4.0
2022-11-12T02:20:46.970Z
2022-11-12T02:20:46.970Z
Greg Miller
<p>I am currently looking into light spectrometers, and I noticed that the ones I found had a similar problem; when the light reaches the spectrometer, it mixes giving a broad range of light wavelengths.</p>
<p>Are there astronomical spectrometers in observatories on Earth or in space telescopes that can measure the spectrum *from a single, specific star separately, i.e. without getting light from other stars contaminating the target star's spectrum?</p>
<p>If so, how do they do it?</p>

CC BY-SA 4.0
2022-11-11T03:30:30.803Z
I don't understand the last sentence of your question. Do you know how spectrometers work? Which did you find and look at to reach your premise of the question, what are the sources of your observations?
planetmaker
CC BY-SA 4.0
2022-11-11T05:24:02.880Z
I just made a general assumption as I have used many spectroscopy programs but this is just a general question. I am just wondering if spectrometers can focus on a small beam of light like a far away star.
Aakarsh Tathachar
CC BY-SA 4.0
2022-11-11T08:20:17.677Z
Would you like to ask "How do astronomical spectrometers measure spectra from single stars separately, without contamination from all of the nearby starts?"
uhoh
CC BY-SA 4.0
2022-11-11T15:39:13.147Z
Yes, that is my question.
Aakarsh Tathachar
CC BY-SA 4.0
2022-11-11T23:56:05.713Z
@AakarshTathachar thanks for your reply! This is a great question! I've adjusted title and text of body a bit to make it a better fit for this site. I dropped the last bit because it wasn't about Astronomy. As you know, you can ask as many (good) questions as you like here or in any of the other SE sites so based on what you learn from answers here you can always ask a follow-up question.
uhoh
CC BY-SA 4.0
2022-11-12T07:50:43.217Z
I don't understand your question. Are you talking about the case of two stars in the same direction or two stars that are clearly separated on the sky?
ProfRob
<observational-astronomy><spectroscopy><optics><instruments><spectrometry>
How do astronomical spectrometers measure spectra from single stars separately, without contamination from all of the nearby stars?
Aakarsh Tathachar
# How do astronomical spectrometers measure spectra from single stars separately, without contamination from all of the nearby stars?

(Asked by: username_0 on 2022-11-11)

I am currently looking into light spectrometers, and I noticed that the ones I found had a similar problem; when the light reaches the spectrometer, it mixes giving a broad range of light wavelengths.

Are there astronomical spectrometers in observatories on Earth or in space telescopes that can measure the spectrum \*from a single, specific star separately, i.e. without getting light from other stars contaminating the target star's spectrum?

If so, how do they do it?

**Tags:** observational-astronomy, spectroscopy, optics, instruments, spectrometry

> **Comments:**
> **username_1**: I don't understand the last sentence of your question. Do you know how spectrometers work? Which did you find and look at to reach your premise of the question, what are the sources of your observations?  
> **username_0**: I just made a general assumption as I have used many spectroscopy programs but this is just a general question. I am just wondering if spectrometers can focus on a small beam of light like a far away star.  
> **username_2**: Would you like to ask "How do astronomical spectrometers measure spectra from single stars separately, without contamination from all of the nearby starts?"  
> **username_0**: Yes, that is my question.  
> **username_2**: @AakarshTathachar thanks for your reply! This is a great question! I've adjusted title and text of body a bit to make it a better fit for this site. I dropped the last bit because it wasn't about Astronomy. As you know, you can ask as many (good) questions as you like here or in any of the other SE sites so based on what you learn from answers here you can always ask a follow-up question.  
> **username_3**: I don't understand your question. Are you talking about the case of two stars in the same direction or two stars that are clearly separated on the sky?  

---

## 1 answers

### Answer by username_4 on 2022-11-12. Score: 5

[![SDSS Plug Plate](https://i.sstatic.net/Mtj2Y.png)](https://i.sstatic.net/Mtj2Y.png)

I imagine it's done differently based on the goals. Anything wanting to study just one object could simply mask out everything else. But the [Sloan Digital Sky Survey](https://www.sdss.org/) studies numerous objects at once. The method they use is to create a "plug plate" corresponding to each object to be studied. A fiber optic cable was attached to each hole and ran to a separate spectrograph to study that object.

The article [SDSS Plates](https://voyages.sdss.org/preflight/sdss-plates/) has more information, including a video on the making of the plates, and another showing the fiber optic hookups.

The image above is the bare plate, and the image below is the plate with the cables hooked up.

[![SDSS Plug Plate with cables](https://i.sstatic.net/gvjc6.jpg)](https://i.sstatic.net/gvjc6.jpg)

> **Comments:**
> **username_0**: This is very helpful but on a satellite I don't think a plug plate is used because the satellite keeps moving and the orientation of the objects changes. Are there any other ways to find the spectra?  
> **username_4**: Telescopes on the ground are also moving, even more so than those in Earth orbit.  A satellite's motion around the Earth will be negligible as long as it maintains its orientation.  But they won't have people there to switch out the plates.  So, as I said above, they're more likely to just mask off everything but one object using an adjustable mask.  
> **username_2**: More about fiber arrays: [How exactly will DESI simultaneously capture individual spectra from 5,000 galaxies using optical fibers?](https://astronomy.stackexchange.com/q/33804/7982) and [What is the dimensions of the smallest object detectable by an optical fiber from a specific distance?](https://astronomy.stackexchange.com/q/29111/7982)  
> **username_2**: Can you support the idea that fibers can be used to capture just one object by adding some quantitative information? This is certainly multimode fiber with a core diameter of at least tens of microns if not hundreds; can you find an actual number and translate to arcseconds? Also, does the far end of the fiber feed the spectrometer directly or is there still a narrow slit at each fiber's output?  
> **username_2**: @AakarshTathachar The big space telescopes do have some amazing guidance systems to keep themselves pointing in the same direction during measurements with very high stability, but there might be other reasons why an optical fiber-based spectrometers are unsuitable for space telescopes. I think you can ask a new question "Have optical fibers ever been used to collect and transfer light in space telescopes?" and you can link back here for background.  
> **username_0**: That is good for more understanding but I was just wondering if this system can identify the main concentration of fire in a forest fire under a cover of trees and smoke. If this technique isn't used, would it be more efficient?  
> **username_5**: @username_2 As mentioned in the first link username_3 provided, the individual fibers have diameters of 3 arc seconds in the case of the original spectrograph and 2 arc seconds for the newer (“BOSS”) spectrograph.  
> **username_5**: @username_2 I’m sorry, I meant username_4’s answer!  
> **username_2**: @PeterErwin okay great! That will be very helpful if moved back into the answer post itself.  

---

