34
votes
Accepted
What detail can Hubble see on Mars?
Forget about magnification. People who know telescopes don't think in terms of magnification. What matters is the angular resolution, or the resolving power: the angular size of the smallest details ...
- 18.1k
13
votes
Accepted
Why aren't ground-based observatories using adaptive optics for visible wavelengths (circa 2016)?
There's a pretty good discussion at this page.
There are several factors at work:
The smaller isoplanatic angle, as you note. This limits how much of the sky you can observe with AO, since your ...
- 16.4k
13
votes
Accepted
Why not build a swarm of space telescopes?
There are a mixture of factors here.
Firstly the telescopes used to photograph the black hole were radio telescopes. Radio-waves are at a low enough frequency that we can process them directly as ...
- 116k
11
votes
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Would Adaptive Optics be Useful in Radio Astronomy?
In fact, the techniques of adaptive optics are already being used in radio astronomy. They are implicit in the basic imaging algorithms (e.g., CLEAN) used to produce maps from radio interferometers. ...
- 154
10
votes
What detail can Hubble see on Mars?
The Hubble space telescope has a 2.4m mirror and is pretty much diffraction limited, so at near-UV wavelengths of say 240nm it has an angular resolution of about $10^{-7}$ radians. Mars' closest ...
- 10.2k
10
votes
Would it be possible to use existing radio-telescopes to do spot measurements of CMB?
Water vapour in the atmosphere emits microwave radiation, which interferes with the observation of the microwave background. For this reason, space telescopes such as COBE or WMAP are best placed to ...
- 116k
9
votes
Accepted
Can Drizzle Integration increase resolution beyond theoretical resolution of telescope?
Drizzling can't actually do any better than the theoretical resolving power of the combination of your telescope and the atmosphere. What it can do is at least partly compensate for having pixels that ...
- 16.4k
9
votes
How does making a refracting telescope very long reduce the chromatic aberration of an uncorrected lens?
The actual math is a bit complicated, but there's a simple intuitive explanation.
Longitudinal chromatic aberration happens because, when you cut a convergent lens in two, and you look at the cross-...
- 18.1k
9
votes
Accepted
Plot of best available resolution vs wavelength - radio through gamma rays?
After a bit of searching, I found this blog page, which has several charts about various observatories, including this one:
Image courtesy of Olaf Frohn under the Creative Commons Attribution-Share ...
- 36k
8
votes
Accepted
How could a 20 inch space telescope "be able to make out Earth-size planets" orbiting Alpha Centauri?
I'm not familiar with the design of the ProjectBlue telescope, but I think you have answered your own question.
The habitable zones for Alpha Cen A and B, are approximately centred at 1.25au and 0....
- 146k
8
votes
Accepted
What is the cause of all of these sharp, concentric rings around bright stars in this HST image?
The diffraction pattern at the focal plane created by a circular aperture is called an Airy Disk or Airy Pattern. Both the outer opening and the inner hole plus secondary contribute to the exact ...
- 3,328
7
votes
Accepted
Can the interferometer called "Gravity" measure "a few centimeters on the Moon"?
A 130m baseline operating at 2 microns gives a theoretical resolution of $2\times 10^{-6}/130$ radians. At a distance of 400,000 km this translates to 6m.
My guess is that Genzel is referring to the ...
- 146k
6
votes
Can Drizzle Integration increase resolution beyond theoretical resolution of telescope?
Drizzling is just one technique in the field of super resolution imaging. Note that claims that you can't "pass the resolution limit" of a camera are wrong, in principle. In practice, it's really hard....
- 2,946
6
votes
Accepted
How would astronomical seeing on Mars differ from that on Earth?
As far as I know, "seeing" (or rather the effects influencing optical wave propagation) is caused by turbulence in the atmosphere.
Using the Reynolds number Number $ Re = \dfrac{\rho L v}{\mu}$ as a ...
- 76
5
votes
Accepted
Under what situations can an aperture mask improve the resolution of a small/medium amateur telescope? Is this demonstrable mathematically?
The vast majority of people - almost everyone, really - should not rely on this on a daily basis. The chances are overwhelming that they will reduce the performance of their instruments. There are so ...
- 18.1k
4
votes
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Why is the opening in the Anglo-Australian Telescope's dome so small?
This is a two part windscreen designed to minimize the effects of windshake on the telescope and to avoid the deterioration in image quality that wind would cause. The AAT is in a tall 6 story dome on ...
- 8,312
4
votes
Accepted
How did VLT's adaptive optics obtain this resolution for Neptune? Is it really working in visible wavelengths?
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 ...
- 146k
4
votes
Why aren't ground-based observatories using adaptive optics for visible wavelengths (circa 2016)?
The simple answer for the wavelength part is that performance of AO systems degrades the shorter in wavelength you look. The basics of what happens is as you go to shorter the wavelengths of light, ...
- 215
4
votes
Accepted
How to find the distance between stars
If you know the distances of both objects to the Earth and the angular separation between them, using the law of cosines is the only reasonable option.
Suppose you know the distances of both objects ...
- 1,720
3
votes
Accepted
Question about Telescopes , observations and explanations of the observations
1. Resolving power and diffraction
Diffraction happens anywhere there's an edge. "It is defined as the bending of light around the corners of an obstacle or aperture into the region of geometrical ...
- 18.1k
3
votes
Question about Telescopes , observations and explanations of the observations
I'll attempt to answer as many of these questions, to the best of my abilities, as I can at this late hour.
1) Lenses have an index of refraction that is different than vacuum, and air, and they are ...
- 736
3
votes
Claim that 30-m class telescopes will have resolution far superior to Hubble: true?
The latest adaptive optics systems now allows diffraction limited images from the 8 meter Very Large Telescope in the visible spectrum. So it seems reasonable that with continued improvements this ...
- 39
3
votes
What would be the maximum theoretically possible angular resolution?
The answer that you are looking for rests on two main pillars. Are you limited in your ability to resolve objects because of the atmosphere like most ground-based telescopes, or because of the ...
- 176
3
votes
Accepted
Do point spread functions from large single telescopes using adaptive optics still look like Airy functions for narrow-band filters?
Yes, narrow-band images taken with adaptive optics on ground-based telescopes produce point-spread functions resembling Airy disks.
To answer this, I went fishing for some data, and randomly caught a ...
- 2,039
2
votes
Accepted
Will the E-ELT use Adaptive Optics at visible wavelengths?
From looking at the E-ELT website, it appears that at first light, the AO will only work for near-IR. Specifically, the instrument that can use AO is the MICADO instrument. The description page for ...
- 15k
2
votes
Accepted
Why is this HST WFPC2 image so much fuzzier than the WFC3 image of the same field?
As Rob Jeffries suggested, in the WFPC2 observations the progenitor star fell located on one of the wide-field ("WF") chips of WFPC2. (I verified this by downloading one of the preview images from the ...
- 16.4k
2
votes
What resolution would earth-moon telescope achieve?
According to Wikipedia, the angular resolution is inversely proportional to the baseline (the separation between the telescopes). The order of magnitude of the baseline of the Event Horizon Telescope ...
- 4,780
2
votes
What is the actual resolution of Event Horizon Telescope?
The resolution of an interferometer at a wavelength $\lambda$ is $\theta\sim\lambda/b$, where $b$ is the longest baseline (distance between two telescopes) in the array. According to the first of this ...
- 36k
Only top scored, non community-wiki answers of a minimum length are eligible