7 ms·

I'm a PhD student working with data of globular clusters from this instrument for quite some time now. I will be happy to answer your questions!

mattlondon 8y ago
I'll bite. In those pictures of neptune, what is the KM-per-pixel were looking at? Is there a minimum focal length on this? Purely hypothetical: Could we basically see astronaut's footprints on the moon with this? What about looking into the window of the ISS?
- m-app 8y ago
  From the FAQ: http://www.eso.org/public/about-eso/faq/faq-vlt-paranal/#18 http://www.eso.org/public/about-eso/faq/faq-vlt-paranal/#18 > Q: Could the VLT take a picture of the Moon-landing sites? > A: Yes, but the images would not be detailed enough to show the equipment left behind by the astronauts. Using its adaptive optics system, the VLT has already taken one of the sharpest ever images of the lunar surface as seen from Earth: http://www.eso.org/public/news/eso0222/ http://www.eso.org/public/news/eso0222/. However, the smallest details visible in this image are still about one hundred metres on the surface of the Moon, while the parts of the lunar modules which are left on the Moon are less than 10 metres in size. A telescope 200 metres in diameter would be needed to show them. [continued]
- eisstrom 8y ago
  In this narrow-field mode of MUSE, the CCD detector can resolve 0.025 arcseconds per pixel (arcsecond is a weird unit for angles used in astronomy). At the current distance to Neptune (according to wolframalpha: about 30 au = 4.5 bn km), this corresponds to about 500 km/px. Due to observing conditions, I think the real resolution was more like 0.07...0.08 arcseconds, so maybe it was 1000 to 2000 km/px. I'm not sure if the focal length plays any role here. The resolution is usually limited by the telescope size (true for all telescopes, scales with 1/diameter) and atmospheric conditions (only relevant for ground based ones). At the distance of the moon (300,000 km), the physical resolution is 36 m/px and for the ISS (400 km) it is 5 cm/px. If you want to play around with it, here's the formula: length_still_resolved = angular_resolution * distance The angular resolution is 1.2 * 10^-7 (= 0.025 arcseconds converted to radian), distance and length_still_resolved have the same units.
appleflaxen 8y ago
the article makes it sound like the approach is so effective that it makes space-based telescopes unnecessary. is that true? does this mean that we should simply use ground-based 'scopes with adaptive optics?
- Tepix 8y ago
  Not if we want to look in the infrared.
- eisstrom 8y ago
  We can achieve a very high resolution from the ground but only in a very small field of view. To cover one typical HST image with MUSE at the VLT, we would need a mosaic of hundreds of exposures. The reason for this are the four artificial guiding stars from the lasers. The closer they are together on the sky, the more atmospheric distortion you can correct. Here is an image of them: https://www.eso.org/public/unitedkingdom/images/vlt-laser-cc2/?lang https://www.eso.org/public/unitedkingdom/images/vlt-laser-cc... Some parts of the electromagnetic spectrum are also not possible to observe from the ground. That's mainly UV and shorter wavelengths (X-ray, gamma-rays). We will always need space telescopes if we want to have these photons.
  - nabla9 8y ago
    Does adding more lasers fix the field of view problem?
    - eisstrom 8y ago
      This is very much unexplored territory, but ESO thinks so. The ELT (https://www.eso.org/public/teles-instr/elt/ https://www.eso.org/public/teles-instr/elt/) will use more lasers but the exact configuration is still work in progress, as far as I know.
    - namibj 8y ago
      Yes. You need one dot for each patch, where the distortion inside each patch is approximately constant inside a single instant. Now, handling these multiple dots in a good way, that's another story. Compare the patch size/discussion in https://publikationen.uni-tuebingen.de/xmlui/handle/10900/49685 https://publikationen.uni-tuebingen.de/xmlui/handle/10900/49...
Jaruzel 8y ago
Are the images natural colour, or have they been 'enhanced' in any way? i.e. is Neptune really that blue?
- eisstrom 8y ago
  The advantage of MUSE is that you get all color information, i. e. the flux at any wavelength from blue to red. In principle, one can use this together with the sensitivity curve for our eyes to construct a natural image. In this case, I think, they tried to imitate the color scheme from the Hubble image which is more limited. In short: Not sure how realistic this is, but one could make a realistic image from the new data.
  - mozumder 8y ago
    So MUSE is hyperspectral? there's a full spectrograph at each pixel?
    - eisstrom 8y ago
      Exactly! One datacube that comes out from the instrument contains 300 x 300 spectra. This is actually the main capability of the instrument which has 24 individual spectrographs. Here's a nice animation of the path the light takes inside MUSE: https://www.youtube.com/watch?v=-fh2Y6Zyhwc&feature=youtu.be&t=378 https://www.youtube.com/watch?v=-fh2Y6Zyhwc&feature=youtu.be...
      - yread 8y ago
        Awe-inspiring. You can see the individual spectrographs at https://youtu.be/-fh2Y6Zyhwc?t=1089 https://youtu.be/-fh2Y6Zyhwc?t=1089
  - vanderZwan 8y ago
    Could one use that information the other way around to make estimates for expected "missing data" in Hubble images taken in areas where VLT has not looked yet, for example to decide where to look next? <something something throw machine learning at it cliché>
vanderZwan 8y ago
> With this new capability, the 8-metre UT4 reaches the theoretical limit of image sharpness and is no longer limited by atmospheric blur. Theoretical limit as in diffraction limited? How will this technology "scale" to other frequencies and resolutions? Related to this diffraction limit: is there any overlap in the advances in microscopy and astronomy? For example, do advances in super-resolution microscopy[0] affect advances in optics in astronomy? Could advances in adaptive optics in astronomy somehow translate to microscopy? (I'm also curious if this technology will make putting telescopes in satellites not worth the cost, but that question was already asked and answered here: https://news.ycombinator.com/item?id=17557482 https://news.ycombinator.com/item?id=17557482) [0] https://en.wikipedia.org/wiki/Super-resolution_microscopy https://en.wikipedia.org/wiki/Super-resolution_microscopy
- eisstrom 8y ago
  Yes, the diffraction limit is meant here. The VLT has four 8 m mirrors, for each of them the angular resolution limit is = wavelength/diameter = 8 * 10^(-8) rad. The practical resolution of the new narrow-field mode is about 4*10^(-7) rad, and it was one order of magnitude larger before. Adaptive optics is the key invention here. As far as I know, it works better in the near-infrared than in the red part of the optical range, and it gets worse toward the blue part. Due to this, our resolution changes as a function of the wavenlength, since MUSE captures the flux from all wavelengths at the same time. ESO wants to achieve an even higher resolution at the 40m Extremely Large Telescope (another order of magnitude better): https://www.eso.org/public/teles-instr/elt/ https://www.eso.org/public/teles-instr/elt/ It's funny that your mention super-resolution microscopy because Stefan Hell, one of the Nobel Prize winners for advances in that field, works in the same city as we do. So far, I don't think we have any overlap with what he does.
  - vanderZwan 8y ago
    > The practical resolution of the new narrow-field mode is about 4 * 10^(-7) rad, and it was one order of magnitude larger before. Amazing! :) > As far as I know, it works better in the near-infrared than in the red part of the optical range, and it gets worse toward the blue part. Do you know what is the reason for this? Noise from Rayleigh scattering? EDIT: Already answered here: https://news.ycombinator.com/item?id=17559121 https://news.ycombinator.com/item?id=17559121 > It's funny that your mention super-resolution microscopy because Stefan Hell, one of the Nobel Prize winners for advances in that field, works in the same city as we do. So far, I don't think we have any overlap with what he does. Why not arrange a kind of meet-up? :) Surely exchanging ideas would lead to interesting ideas, and in the worst case you can at least by inspired by geeking out over mega- and micro-optics together.
anon1253 8y ago
How does it compare to my amateur attempts with a 12" Newton https://www.flickr.com/photos/joelkuiper/42502865635/ https://www.flickr.com/photos/joelkuiper/42502865635/ :p ? All kidding aside, do you think there is some scientific value in the efforts of hobby astronomers and astrophotographers around the world?
- zfedoran 8y ago
  I gotta say I'm quite jealous of your dark skies and beautiful photography. Also, how are you overcoming flexure and mirror flop with your setup!? I have troubles keeping a 6" stable for a minute with a reasonable mount. Do you have more info on your setup anywhere?
arriu 8y ago
Can you tell us about your favourite globular clusters? I know some of them have very interesting properties like having similar stellar ages but are there any really peculiar ones you can tell us about? Also, I'd love to see some of the images your referring to. Thanks!
- eisstrom 8y ago
  I like NGC 3201 because we found a stellar mass black hole in it (https://www.eso.org/public/news/eso1802/ https://www.eso.org/public/news/eso1802/). There should be many more of them in all clusters, but they are hard to find. Theorists can use this to check their N-body simulations of globular clusters. Some clusters (omega Cen, 47 Tuc) are really weird and different from all others. We think that they might be the remnant cores of dwarf galaxies. What images do you mean?

mattlondon 8y ago

I'll bite. In those pictures of neptune, what is the KM-per-pixel were looking at? Is there a minimum focal length on this? Purely hypothetical: Could we basically see astronaut's footprints on the moon with this? What about looking into the window of the ISS?

m-app 8y ago
From the FAQ: http://www.eso.org/public/about-eso/faq/faq-vlt-paranal/#18 http://www.eso.org/public/about-eso/faq/faq-vlt-paranal/#18 > Q: Could the VLT take a picture of the Moon-landing sites? > A: Yes, but the images would not be detailed enough to show the equipment left behind by the astronauts. Using its adaptive optics system, the VLT has already taken one of the sharpest ever images of the lunar surface as seen from Earth: http://www.eso.org/public/news/eso0222/ http://www.eso.org/public/news/eso0222/. However, the smallest details visible in this image are still about one hundred metres on the surface of the Moon, while the parts of the lunar modules which are left on the Moon are less than 10 metres in size. A telescope 200 metres in diameter would be needed to show them. [continued]
eisstrom 8y ago
In this narrow-field mode of MUSE, the CCD detector can resolve 0.025 arcseconds per pixel (arcsecond is a weird unit for angles used in astronomy). At the current distance to Neptune (according to wolframalpha: about 30 au = 4.5 bn km), this corresponds to about 500 km/px. Due to observing conditions, I think the real resolution was more like 0.07...0.08 arcseconds, so maybe it was 1000 to 2000 km/px. I'm not sure if the focal length plays any role here. The resolution is usually limited by the telescope size (true for all telescopes, scales with 1/diameter) and atmospheric conditions (only relevant for ground based ones). At the distance of the moon (300,000 km), the physical resolution is 36 m/px and for the ISS (400 km) it is 5 cm/px. If you want to play around with it, here's the formula: length_still_resolved = angular_resolution * distance The angular resolution is 1.2 * 10^-7 (= 0.025 arcseconds converted to radian), distance and length_still_resolved have the same units.

appleflaxen 8y ago

the article makes it sound like the approach is so effective that it makes space-based telescopes unnecessary. is that true? does this mean that we should simply use ground-based 'scopes with adaptive optics?

Tepix 8y ago
Not if we want to look in the infrared.
eisstrom 8y ago
We can achieve a very high resolution from the ground but only in a very small field of view. To cover one typical HST image with MUSE at the VLT, we would need a mosaic of hundreds of exposures. The reason for this are the four artificial guiding stars from the lasers. The closer they are together on the sky, the more atmospheric distortion you can correct. Here is an image of them: https://www.eso.org/public/unitedkingdom/images/vlt-laser-cc2/?lang https://www.eso.org/public/unitedkingdom/images/vlt-laser-cc... Some parts of the electromagnetic spectrum are also not possible to observe from the ground. That's mainly UV and shorter wavelengths (X-ray, gamma-rays). We will always need space telescopes if we want to have these photons.
- nabla9 8y ago
  Does adding more lasers fix the field of view problem?
  - eisstrom 8y ago
    This is very much unexplored territory, but ESO thinks so. The ELT (https://www.eso.org/public/teles-instr/elt/ https://www.eso.org/public/teles-instr/elt/) will use more lasers but the exact configuration is still work in progress, as far as I know.
  - namibj 8y ago
    Yes. You need one dot for each patch, where the distortion inside each patch is approximately constant inside a single instant. Now, handling these multiple dots in a good way, that's another story. Compare the patch size/discussion in https://publikationen.uni-tuebingen.de/xmlui/handle/10900/49685 https://publikationen.uni-tuebingen.de/xmlui/handle/10900/49...

Jaruzel 8y ago

Are the images natural colour, or have they been 'enhanced' in any way? i.e. is Neptune really that blue?

eisstrom 8y ago
The advantage of MUSE is that you get all color information, i. e. the flux at any wavelength from blue to red. In principle, one can use this together with the sensitivity curve for our eyes to construct a natural image. In this case, I think, they tried to imitate the color scheme from the Hubble image which is more limited. In short: Not sure how realistic this is, but one could make a realistic image from the new data.
- mozumder 8y ago
  So MUSE is hyperspectral? there's a full spectrograph at each pixel?
  - eisstrom 8y ago
    Exactly! One datacube that comes out from the instrument contains 300 x 300 spectra. This is actually the main capability of the instrument which has 24 individual spectrographs. Here's a nice animation of the path the light takes inside MUSE: https://www.youtube.com/watch?v=-fh2Y6Zyhwc&feature=youtu.be&t=378 https://www.youtube.com/watch?v=-fh2Y6Zyhwc&feature=youtu.be...
    - yread 8y ago
      Awe-inspiring. You can see the individual spectrographs at https://youtu.be/-fh2Y6Zyhwc?t=1089 https://youtu.be/-fh2Y6Zyhwc?t=1089
- vanderZwan 8y ago
  Could one use that information the other way around to make estimates for expected "missing data" in Hubble images taken in areas where VLT has not looked yet, for example to decide where to look next? <something something throw machine learning at it cliché>

vanderZwan 8y ago

> With this new capability, the 8-metre UT4 reaches the theoretical limit of image sharpness and is no longer limited by atmospheric blur. Theoretical limit as in diffraction limited? How will this technology "scale" to other frequencies and resolutions? Related to this diffraction limit: is there any overlap in the advances in microscopy and astronomy? For example, do advances in super-resolution microscopy[0] affect advances in optics in astronomy? Could advances in adaptive optics in astronomy somehow translate to microscopy? (I'm also curious if this technology will make putting telescopes in satellites not worth the cost, but that question was already asked and answered here: https://news.ycombinator.com/item?id=17557482 https://news.ycombinator.com/item?id=17557482) [0] https://en.wikipedia.org/wiki/Super-resolution_microscopy https://en.wikipedia.org/wiki/Super-resolution_microscopy

eisstrom 8y ago
Yes, the diffraction limit is meant here. The VLT has four 8 m mirrors, for each of them the angular resolution limit is = wavelength/diameter = 8 * 10^(-8) rad. The practical resolution of the new narrow-field mode is about 4*10^(-7) rad, and it was one order of magnitude larger before. Adaptive optics is the key invention here. As far as I know, it works better in the near-infrared than in the red part of the optical range, and it gets worse toward the blue part. Due to this, our resolution changes as a function of the wavenlength, since MUSE captures the flux from all wavelengths at the same time. ESO wants to achieve an even higher resolution at the 40m Extremely Large Telescope (another order of magnitude better): https://www.eso.org/public/teles-instr/elt/ https://www.eso.org/public/teles-instr/elt/ It's funny that your mention super-resolution microscopy because Stefan Hell, one of the Nobel Prize winners for advances in that field, works in the same city as we do. So far, I don't think we have any overlap with what he does.
- vanderZwan 8y ago
  > The practical resolution of the new narrow-field mode is about 4 * 10^(-7) rad, and it was one order of magnitude larger before. Amazing! :) > As far as I know, it works better in the near-infrared than in the red part of the optical range, and it gets worse toward the blue part. Do you know what is the reason for this? Noise from Rayleigh scattering? EDIT: Already answered here: https://news.ycombinator.com/item?id=17559121 https://news.ycombinator.com/item?id=17559121 > It's funny that your mention super-resolution microscopy because Stefan Hell, one of the Nobel Prize winners for advances in that field, works in the same city as we do. So far, I don't think we have any overlap with what he does. Why not arrange a kind of meet-up? :) Surely exchanging ideas would lead to interesting ideas, and in the worst case you can at least by inspired by geeking out over mega- and micro-optics together.

anon1253 8y ago

How does it compare to my amateur attempts with a 12" Newton https://www.flickr.com/photos/joelkuiper/42502865635/ https://www.flickr.com/photos/joelkuiper/42502865635/ :p ? All kidding aside, do you think there is some scientific value in the efforts of hobby astronomers and astrophotographers around the world?

zfedoran 8y ago
I gotta say I'm quite jealous of your dark skies and beautiful photography. Also, how are you overcoming flexure and mirror flop with your setup!? I have troubles keeping a 6" stable for a minute with a reasonable mount. Do you have more info on your setup anywhere?

arriu 8y ago

Can you tell us about your favourite globular clusters? I know some of them have very interesting properties like having similar stellar ages but are there any really peculiar ones you can tell us about? Also, I'd love to see some of the images your referring to. Thanks!

eisstrom 8y ago
I like NGC 3201 because we found a stellar mass black hole in it (https://www.eso.org/public/news/eso1802/ https://www.eso.org/public/news/eso1802/). There should be many more of them in all clusters, but they are hard to find. Theorists can use this to check their N-body simulations of globular clusters. Some clusters (omega Cen, 47 Tuc) are really weird and different from all others. We think that they might be the remnant cores of dwarf galaxies. What images do you mean?