<p>It is an image taken with the new narrow field mode of the MUSE instrument using the GALACSI Adaptive optics module on a single (UT4) VLT telescope using laser guide stars.</p>

<p>I am having a great deal of difficulty (e.g. from <a href="http://www.eso.org/public/news/eso1824/" rel="nofollow noreferrer">this press release</a>) in working out at what wavelength(s) this image was taken. I do not believe that the AO system is working at blue wavelengths and therefore the comparison with HST (which certainly does) is somewhat misleading. I think (<a href="https://www.eso.org/sci/facilities/paranal/instruments/muse/inst.html" rel="nofollow noreferrer">from ESO's own instrumentation pages</a>) that the MUSE narrow field mode has zero efficiency at blue wavelengths and the description of <a href="https://www.eso.org/sci/facilities/develop/ao/sys/galacsi.html" rel="nofollow noreferrer">GALACSI</a> only talks about AO correction approaching diffraction limited images at 650 nm (i.e. red wavelengths).</p>

<p>The captioning to the press release images found <a href="http://www.eso.org/public/images/eso1824a/" rel="nofollow noreferrer">here</a> suggest that the shortest wavelengths used in this <strong>false-colour image</strong> were 550nm and that most of the detail you see is coming from redder wavelengths (600-920nm).</p>

CC BY-SA 4.0
2018-07-19T00:35:00.880Z
Thanks for looking into this and writing a well-sourced answer! There is a lot of really good material to read here. As far as the collor, the situation reminds me a bit of what happened with [Is the “Mars blue dune” actually blue? And what makes it so?](https://space.stackexchange.com/q/28082/12102)
uhoh
CC BY-SA 4.0
2018-10-27T15:13:51.283Z
Indeed, MUSE has zero efficiency (in any of its modes) blueward of about 480nm; it's one of the few deficiencies of an otherwise amazing instrument.
Peter Erwin
CC BY-SA 4.0
2021-06-23T01:25:38.887Z
fyi I've just quoted some of this in [What capabilities of Hubble are unique and irreplaceable? What can it do that simply can't be done by any other ground or space-based telescope?]()https://astronomy.stackexchange.com/q/44503/7982)
uhoh
CC BY-SA 4.0
2023-05-17T03:50:32.617Z
Generally "true color" is *hard*. Computer monitors are very limited in terms of producing pure colors and are different from each-other. Eyes are also varied (see: https://www.exploratorium.edu/video/paul-doherty-disagreeing-about-color). Not to mention the small percentage who are tetra-chromatic.

For accurate true color, one may need to measure 12 channels in the visible and reproduce those wavelengths in a special laser projector.
Kevin Kostlan
CC BY-SA 4.0
2018-07-18T19:34:10.340Z
2018-07-18T19:41:51.663Z
2018-07-18T19:41:51.663Z
ProfRob
<p>This image of Neptune taken with the VLT is really impressive. The resolution is achieved by recent improvements in the adaptive optics.</p>

<ul>
<li>Gizmodo: <a href="https://gizmodo.com/new-super-crisp-images-of-neptune-show-how-far-our-tele-1827683475" rel="noreferrer">New Super-Crisp Images of Neptune Show How Far Our Telescopes Have Come</a></li>
<li>Space.com <a href="https://www.space.com/41202-new-adaptive-optics-produces-stunning-views.html" rel="noreferrer">Telescope Upgrade Produces Stunningly Clear Views of Space</a></li>
</ul>

<p>But I don't really understand, is this coming from just one 8 meter mirror, or is this using more than one of the four that make up the VLT? Also, is this really using adaptive optics <em>that work in the visible, including blue wavelengths?</em> Or is this a false-color image? See the excellent answer(s) to <a href="https://astronomy.stackexchange.com/q/14795/7982">Why (actually) aren't ground-based observatories using adaptive optics for visible wavelengths?</a></p>

<p><a href="https://i.sstatic.net/me10Y.jpg" rel="noreferrer"><img src="https://i.sstatic.net/me10Y.jpg" alt="Neptune VLT new adaptive optics"></a></p>

<observational-astronomy><neptune><angular-resolution><adaptive-optics><very-large-telescope>
How did VLT's adaptive optics obtain this resolution for Neptune? Is it really working in visible wavelengths?
uhoh
# How did VLT's adaptive optics obtain this resolution for Neptune? Is it really working in visible wavelengths?

(Asked by: username_0 on 2018-07-18)

This image of Neptune taken with the VLT is really impressive. The resolution is achieved by recent improvements in the adaptive optics.

* Gizmodo: [New Super-Crisp Images of Neptune Show How Far Our Telescopes Have Come](https://gizmodo.com/new-super-crisp-images-of-neptune-show-how-far-our-tele-1827683475)
* Space.com [Telescope Upgrade Produces Stunningly Clear Views of Space](https://www.space.com/41202-new-adaptive-optics-produces-stunning-views.html)

But I don't really understand, is this coming from just one 8 meter mirror, or is this using more than one of the four that make up the VLT? Also, is this really using adaptive optics *that work in the visible, including blue wavelengths?* Or is this a false-color image? See the excellent answer(s) to [Why (actually) aren't ground-based observatories using adaptive optics for visible wavelengths?](https://astronomy.stackexchange.com/q/14795/7982)

[![Neptune VLT new adaptive optics](https://i.sstatic.net/me10Y.jpg)](https://i.sstatic.net/me10Y.jpg)

**Tags:** observational-astronomy, neptune, angular-resolution, adaptive-optics, very-large-telescope


---

## 1 answers

### Answer by username_1 on 2018-07-18. Score: 4 | Accepted answer

It is an image taken with the new narrow field mode of the MUSE instrument using the GALACSI Adaptive optics module on a single (UT4) VLT telescope using laser guide stars.

I am having a great deal of difficulty (e.g. from [this press release](http://www.eso.org/public/news/eso1824/)) in working out at what wavelength(s) this image was taken. I do not believe that the AO system is working at blue wavelengths and therefore the comparison with HST (which certainly does) is somewhat misleading. I think ([from ESO's own instrumentation pages](https://www.eso.org/sci/facilities/paranal/instruments/muse/inst.html)) that the MUSE narrow field mode has zero efficiency at blue wavelengths and the description of [GALACSI](https://www.eso.org/sci/facilities/develop/ao/sys/galacsi.html) only talks about AO correction approaching diffraction limited images at 650 nm (i.e. red wavelengths).

The captioning to the press release images found [here](http://www.eso.org/public/images/eso1824a/) suggest that the shortest wavelengths used in this **false-colour image** were 550nm and that most of the detail you see is coming from redder wavelengths (600-920nm).

> **Comments:**
> **username_0**: Thanks for looking into this and writing a well-sourced answer! There is a lot of really good material to read here. As far as the collor, the situation reminds me a bit of what happened with [Is the “Mars blue dune” actually blue? And what makes it so?](https://space.stackexchange.com/q/28082/12102)  
> **username_2**: Indeed, MUSE has zero efficiency (in any of its modes) blueward of about 480nm; it's one of the few deficiencies of an otherwise amazing instrument.  
> **username_0**: fyi I've just quoted some of this in [What capabilities of Hubble are unique and irreplaceable? What can it do that simply can't be done by any other ground or space-based telescope?]()https://astronomy.stackexchange.com/q/44503/7982)  
> **username_3**: Generally "true color" is *hard*. Computer monitors are very limited in terms of producing pure colors and are different from each-other. Eyes are also varied (see: https://www.exploratorium.edu/video/paul-doherty-disagreeing-about-color). Not to mention the small percentage who are tetra-chromatic.  For accurate true color, one may need to measure 12 channels in the visible and reproduce those wavelengths in a special laser projector.  

---

