6 ms·

How to Discover a Galaxy with a Telephoto Lens

142 points by bootload 11y ago

acqq 11y ago
The paper by Dragonfly designers: http://arxiv.org/abs/1401.5473 http://arxiv.org/abs/1401.5473 It's not "just" the off-the shelf lenses and cameras, although the lenses are really the crucial part and they are very cleverly used, achieving up to then never achieved low light scattering. At the time it used only 8 lenses, the telescope had weight of more than 100 kg. Here's the robotic mount they used then: http://www.bisque.com/sc/pages/ParamountMEII.aspx http://www.bisque.com/sc/pages/ParamountMEII.aspx The paper with the first results from the Dragonfly: http://iopscience.iop.org/article/10.1088/2041-8205/782/2/L24/meta http://iopscience.iop.org/article/10.1088/2041-8205/782/2/L2...
- PhantomGremlin 11y ago
  Thanks for those links. The paper by the designers is so much better than the incredibly dumbed down fluff in the article. As I read the article I kept thinking things like "what Canon lens?", and "what are the details of the coating?". The paper has a wealth of technical information on all of this.
- dharma1 11y ago
  The paper mentions "science grade CCD sensors" - are these really better than some of the new ultra low light CMOS cameras from Sony and Canon?
  - Cerium 11y ago
    My understanding is that "science grade CCD sensors" have thermal controls to ensure the thermal noise is constant.
  - knappe 11y ago
    More than likely. Most "science" grade CCD sensors, at least in the Astronomy world, are in fact shaved down to make them even more sensitive.
  - aggie 11y ago
    The sensors used are Kodak KAF8300, which are a stand-alone sensor that you hook up to a laptop. They are designed specifically for astronomy, and perform better in some ways than typical consumer cameras. DSLRs that are marketed as tuned for astrophotography often have better sensitivity to certain key wavelengths than their standard counterparts (especially hydrogen-alpha at 656nm), but are missing other benefits of 'science-grade sensors'. "Astronomical CCD cameras are a whole different world from DSLR cameras. These are cameras designed exclusively for AP, and most offer active cooling. The nature of a CCD vs a CMOS sensor in a DSLR results in a camera that is higher sensitivity, but also higher noise. Many Astro CCD cameras have mono sensors (no bayer color layer) which means they are used with filter wheels with different colored filters to capture a natural color image. They can also be used with various narrow-band filters to capture light outside the visible spectrum." from http://soggyastronomer.com/the-best-dslr-cameras-for-astrophotography/ http://soggyastronomer.com/the-best-dslr-cameras-for-astroph...
    - dharma1 11y ago
      Nice. Did a bit of reading on this, looks like high as possible quantum efficiency (across a broad spectrum) is what is desired. You are right, most DSLR cameras lose about half of the QE to the rgb filters.
- YesProcrast 11y ago
  Footnote 20 is wonderful.
stcredzero 11y ago
They were also frustrated with how cumbersome astronomy had become: Modern astronomical projects are typically large-scale affairs, requiring a small fortune, a mountain of paperwork, and plenty of patience. “You have to envision ways to get $10 million and put a team together, and even then, you only know if things will come to fruition a decade later,” says Abraham, a professor at the University of Toronto. Sounds like big company software development.
antognini 11y ago
Ultimately the reason these small telescopes are so useful for finding these faint, diffuse galaxies is because the surface brightness of an object is independent of the collecting area. Larger optical telescopes have much better resolution, so the amount of light detected from a diffuse galaxy is fairly similar per pixel to a little telescope like Dragonfly. But a little telescope costs probably about three orders of magnitude less than a big telescope and you can afford to hammer a particular target night after night, whereas you'd be lucky to have an hour of time on a large telescope. There are a number of other great small-telescope projects in different areas of astronomy. The one closest to my heart is ASAS-SN (pronounced "Assassin") since it was the idea of the professor across the hall from me when I was at Ohio State and an officemate of mine was the one who spent much of his graduate career building it. The idea was to get a little telescope (like Dragonfly it's pretty much just a telephoto lens with a detector attached) and then have it look at ~1/3 of the sky every night. That way if a supernova goes off in a nearby galaxy (or there is some other transient) it's discovered within a few days. Just this month they published a paper on the discovery of the brightest supernova ever observed [1]. They currently discover more supernovae than all other groups combined (including amateur astronomers, who are a formidable force!). There's another small-telescope project built to search for exoplanets called KELT (the Kilodegree Extremely Little Telescope). Since transiting planets are generally detected around bright stars (at least in apparent magnitude), telescope size is not so important for their discovery. In fact, having too big a telescope can be an issue because the host star is so bright that it saturates the detector. So far they've discovered (I think) somewhere around a dozen planets, though my favorite is Kelt-4Ab because it's in a triple star system (and also because I'm on the paper) [2]. [1]: https://en.wikipedia.org/wiki/ASASSN-15lh https://en.wikipedia.org/wiki/ASASSN-15lh [2]: http://arxiv.org/abs/1510.00015 http://arxiv.org/abs/1510.00015
- stcredzero 11y ago
  But a little telescope costs probably about three orders of magnitude less than a big telescope and you can afford to hammer a particular target night after night, whereas you'd be lucky to have an hour of time on a large telescope. Precisely why PCs/workstations revolutionized research/individual analyst computing.
vvanders 11y ago
Taking two expensive hobbies(photo + astro) and combining them! Also my jaw dropped a bit when I saw all those white telephotos packed together, that's a lot of glass!
- ajross 11y ago
  Only one hobby. These folks are professional astronomers.
so_edgy_n_dark 11y ago
Why. Why do journalists insist on describing "dark matter" by qualifying it with statements like: that mysterious, unseen counterpart to ordinary, luminous matter Dark matter is just shit that ain't burning. It's not mysterious. It's not "spooky actions at a distance", it's not galaxy devouring black hole matter. It's not depressed, or angry, or crazy. It's not an angst-ridden high school teenager. It's just opaque dirt. Or water. Or rocks. Or whatever. Luminous spheres of raw nuclear fusion are much less "ordinary" than the rest of the matter in the universe.
- benjaminjackman 11y ago
  No that's a misconception of what dark matter is. It's weirder than that, it neither emits nor absorbs light, which 'opaque dirt' does. Per Wikipedia: For many decades, astronomers assumed that dark matter was made of the same baryons (protons and neutrons) as all other known matter, but in a form that had been overlooked because it was non-luminous. It could not be in the form of a diffuse gas or dust, as that would be apparent when backlit by visible stars, but searches were organized for other astronomical bodies emitting little or no electromagnetic radiation such as massive compact halo objects. However, evidence eventually accumulated that baryonic dark matter could only account for a small fraction of the missing mass. The study of nucleosynthesis in the Big Bang gives an upper bound on the amount of baryonic matter in the universe,[20] which indicates that the vast majority of dark matter in the universe cannot be baryons, and thus does not form atoms. It also cannot interact with ordinary matter via electromagnetic forces; in particular, dark matter particles do not carry any electric charge.
clockworkelf 11y ago
Why do all the stars disappear at very high altitudes?

142 points by bootload 11y ago

acqq 11y ago

The paper by Dragonfly designers: http://arxiv.org/abs/1401.5473 http://arxiv.org/abs/1401.5473 It's not "just" the off-the shelf lenses and cameras, although the lenses are really the crucial part and they are very cleverly used, achieving up to then never achieved low light scattering. At the time it used only 8 lenses, the telescope had weight of more than 100 kg. Here's the robotic mount they used then: http://www.bisque.com/sc/pages/ParamountMEII.aspx http://www.bisque.com/sc/pages/ParamountMEII.aspx The paper with the first results from the Dragonfly: http://iopscience.iop.org/article/10.1088/2041-8205/782/2/L24/meta http://iopscience.iop.org/article/10.1088/2041-8205/782/2/L2...

PhantomGremlin 11y ago
Thanks for those links. The paper by the designers is so much better than the incredibly dumbed down fluff in the article. As I read the article I kept thinking things like "what Canon lens?", and "what are the details of the coating?". The paper has a wealth of technical information on all of this.
dharma1 11y ago
The paper mentions "science grade CCD sensors" - are these really better than some of the new ultra low light CMOS cameras from Sony and Canon?
- Cerium 11y ago
  My understanding is that "science grade CCD sensors" have thermal controls to ensure the thermal noise is constant.
- knappe 11y ago
  More than likely. Most "science" grade CCD sensors, at least in the Astronomy world, are in fact shaved down to make them even more sensitive.
- aggie 11y ago
  The sensors used are Kodak KAF8300, which are a stand-alone sensor that you hook up to a laptop. They are designed specifically for astronomy, and perform better in some ways than typical consumer cameras. DSLRs that are marketed as tuned for astrophotography often have better sensitivity to certain key wavelengths than their standard counterparts (especially hydrogen-alpha at 656nm), but are missing other benefits of 'science-grade sensors'. "Astronomical CCD cameras are a whole different world from DSLR cameras. These are cameras designed exclusively for AP, and most offer active cooling. The nature of a CCD vs a CMOS sensor in a DSLR results in a camera that is higher sensitivity, but also higher noise. Many Astro CCD cameras have mono sensors (no bayer color layer) which means they are used with filter wheels with different colored filters to capture a natural color image. They can also be used with various narrow-band filters to capture light outside the visible spectrum." from http://soggyastronomer.com/the-best-dslr-cameras-for-astrophotography/ http://soggyastronomer.com/the-best-dslr-cameras-for-astroph...
  - dharma1 11y ago
    Nice. Did a bit of reading on this, looks like high as possible quantum efficiency (across a broad spectrum) is what is desired. You are right, most DSLR cameras lose about half of the QE to the rgb filters.
YesProcrast 11y ago
Footnote 20 is wonderful.

stcredzero 11y ago

They were also frustrated with how cumbersome astronomy had become: Modern astronomical projects are typically large-scale affairs, requiring a small fortune, a mountain of paperwork, and plenty of patience. “You have to envision ways to get $10 million and put a team together, and even then, you only know if things will come to fruition a decade later,” says Abraham, a professor at the University of Toronto. Sounds like big company software development.

antognini 11y ago

Ultimately the reason these small telescopes are so useful for finding these faint, diffuse galaxies is because the surface brightness of an object is independent of the collecting area. Larger optical telescopes have much better resolution, so the amount of light detected from a diffuse galaxy is fairly similar per pixel to a little telescope like Dragonfly. But a little telescope costs probably about three orders of magnitude less than a big telescope and you can afford to hammer a particular target night after night, whereas you'd be lucky to have an hour of time on a large telescope. There are a number of other great small-telescope projects in different areas of astronomy. The one closest to my heart is ASAS-SN (pronounced "Assassin") since it was the idea of the professor across the hall from me when I was at Ohio State and an officemate of mine was the one who spent much of his graduate career building it. The idea was to get a little telescope (like Dragonfly it's pretty much just a telephoto lens with a detector attached) and then have it look at ~1/3 of the sky every night. That way if a supernova goes off in a nearby galaxy (or there is some other transient) it's discovered within a few days. Just this month they published a paper on the discovery of the brightest supernova ever observed [1]. They currently discover more supernovae than all other groups combined (including amateur astronomers, who are a formidable force!). There's another small-telescope project built to search for exoplanets called KELT (the Kilodegree Extremely Little Telescope). Since transiting planets are generally detected around bright stars (at least in apparent magnitude), telescope size is not so important for their discovery. In fact, having too big a telescope can be an issue because the host star is so bright that it saturates the detector. So far they've discovered (I think) somewhere around a dozen planets, though my favorite is Kelt-4Ab because it's in a triple star system (and also because I'm on the paper) [2]. [1]: https://en.wikipedia.org/wiki/ASASSN-15lh https://en.wikipedia.org/wiki/ASASSN-15lh [2]: http://arxiv.org/abs/1510.00015 http://arxiv.org/abs/1510.00015

stcredzero 11y ago
But a little telescope costs probably about three orders of magnitude less than a big telescope and you can afford to hammer a particular target night after night, whereas you'd be lucky to have an hour of time on a large telescope. Precisely why PCs/workstations revolutionized research/individual analyst computing.

vvanders 11y ago

Taking two expensive hobbies(photo + astro) and combining them! Also my jaw dropped a bit when I saw all those white telephotos packed together, that's a lot of glass!

ajross 11y ago
Only one hobby. These folks are professional astronomers.

so_edgy_n_dark 11y ago

Why. Why do journalists insist on describing "dark matter" by qualifying it with statements like: that mysterious, unseen counterpart to ordinary, luminous matter Dark matter is just shit that ain't burning. It's not mysterious. It's not "spooky actions at a distance", it's not galaxy devouring black hole matter. It's not depressed, or angry, or crazy. It's not an angst-ridden high school teenager. It's just opaque dirt. Or water. Or rocks. Or whatever. Luminous spheres of raw nuclear fusion are much less "ordinary" than the rest of the matter in the universe.

benjaminjackman 11y ago
No that's a misconception of what dark matter is. It's weirder than that, it neither emits nor absorbs light, which 'opaque dirt' does. Per Wikipedia: For many decades, astronomers assumed that dark matter was made of the same baryons (protons and neutrons) as all other known matter, but in a form that had been overlooked because it was non-luminous. It could not be in the form of a diffuse gas or dust, as that would be apparent when backlit by visible stars, but searches were organized for other astronomical bodies emitting little or no electromagnetic radiation such as massive compact halo objects. However, evidence eventually accumulated that baryonic dark matter could only account for a small fraction of the missing mass. The study of nucleosynthesis in the Big Bang gives an upper bound on the amount of baryonic matter in the universe,[20] which indicates that the vast majority of dark matter in the universe cannot be baryons, and thus does not form atoms. It also cannot interact with ordinary matter via electromagnetic forces; in particular, dark matter particles do not carry any electric charge.

clockworkelf 11y ago

Why do all the stars disappear at very high altitudes?