36 votes

Is there any role today that would justify building a large single dish radio telescope to replace Arecibo?

Arecibo wasn't just a radio telescope, it was a radar telescope, bouncing megawatt-level radio signals off various bodies in the Solar System. A single-dish transmitter is far superior to a phased-...
Mark's user avatar
  • 3,103
35 votes
Accepted

What will succeed the Arecibo Observatory?

There's no simple answer. In the immediate future, different radio telescopes around the world will pick up the slack in various ways; how that happens will depend on the needs of individual observers ...
HDE 226868's user avatar
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29 votes
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Can I sense a bright star pointing an eight foot antenna towards it?

Stars are too dim for amateur radio equipment. There are two possible radio sources that you can detect: the sun and Jupiter. Jupiter is particularly interesting as interactions between Io and its ...
James K's user avatar
  • 118k
25 votes

Is there any role today that would justify building a large single dish radio telescope to replace Arecibo?

Having a large dish gives you a large collecting area and hence better sensitivity. Building a multitude of receivers with the same collecting area, each having its own feed and electronics, is more ...
ProfRob's user avatar
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24 votes
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How did Arecibo detect methane lakes on Titan, and image Saturn's rings?

Titan "lakes": Published Open Access in Science: Radar Evidence for Liquid Surfaces on Titan Campbell, D. B., Black, G. J., Carter, L. M., and Ostro, S. J., Science 302, 5644, pp. 431-434, 17 Oct ...
uhoh's user avatar
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24 votes

How are radio telescopes pointed?

Well, even most optical telescopes aren't steered by hand and guided by human eyes - aside from a small fraction of objects, most sources are too dim to be seen by the naked eye or even with ...
HDE 226868's user avatar
  • 36.3k
24 votes

"Next Generation Arecibo Telescope (NGAT)... would combine a 314-metre-wide platform with a swarm of 9-metre dishes on top" What would that look like?

There are a few diagrams in the original white paper (Anish Roshi et al. 2021; see Fig. 11) and the revised NGAT-130 proposal (Anish Roshi et al. 2023; see Fig. 3), depicting the basic arrangement. ...
HDE 226868's user avatar
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23 votes
Accepted

A "strange" unit radio astronomy

I would expect the authors to be talking about the signal in terms of janskys, the now-commonly-used units of flux density. The typical definition is $$1\text{ Jansky}=10^{-26}\text{ Watts meters}^{-2}...
HDE 226868's user avatar
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20 votes

Why does the Fourier transform of this CMB image have a hole in it?

Having now looked at the paper by Aiola et al. (2020), it emerges that for that map, they filtered the data to exclude low frequency multipoles with $|l|<150$, corresponding to about 1 degree. This ...
ProfRob's user avatar
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19 votes
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Why does the Fourier transform of this CMB image have a hole in it?

For that specific E-mode map we have applied a Wiener filter to highlight the high SN modes (those "rings"). I also further apply the following filter: $((1 + (kx/5)^{-4})^{-1}) * ((1 + (k/...
Simone Aiola's user avatar
18 votes

Has radio astronomy ever been done on objects that appear very close to the Moon? Is this avoided?

Yes, and lunar occultations have proved useful in several cases. Hazard et al. 1963 used a lunar occultation to produce a high-resolution brightness profile of the now well-studied radio quasar 3C ...
HDE 226868's user avatar
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18 votes
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Is there any role today that would justify building a large single dish radio telescope to replace Arecibo?

Single-dish telescopes have advantages over interferometers in a few areas; existing answers have touched on some of them. Collecting area is extremely important, as Rob Jeffries mentioned, and you ...
HDE 226868's user avatar
  • 36.3k
17 votes

How big a dish do I need for radio astronomy?

I am a member of Astropeiler Stockert e.V., and we are fortunate enough to be able to approach this problem coming from the "large side" :-) We have a 25m, 10m and 3m telescopes as well as an ...
jstarek's user avatar
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16 votes
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What does the velocity dispersion of a galaxy mean?

Definition of the velocity dispersion From the title of your question, I'm unsure whether you actually know what "dispersion" means: The dispersion of some numbers is the spread around their mean, ...
pela's user avatar
  • 37.6k
15 votes

Building a floating, ocean-going giant radio telescope?

I would be extremely concerned about the ability of such a telescope to make adequately precise measurements, given the motion of the water. The leading radio telescopes have their mirrors and ...
HDE 226868's user avatar
  • 36.3k
14 votes

Do radio telescopes see other stars better at night?

The Sun doesn't substantially impact radio observations during the day, because radio telescopes operate at long wavelengths. In general, light at longer wavelengths scatters less than light at ...
HDE 226868's user avatar
  • 36.3k
13 votes
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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 ...
Peter Erwin's user avatar
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13 votes
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Why does the Sun deviate from a typical blackbody spectrum in the S band?

There are other ways of getting emissions than just direct thermal radiation. Most of it happens through plasma interactions in the solar corona and atmosphere than in the chromosphere. This review ...
Anders Sandberg's user avatar
13 votes

What will succeed the Arecibo Observatory?

As you said, the loss of Arecibo will definitely put a dent in the field of radio astronomy. As for what will help take its place - there are a couple options. Green Bank Observatory has been and ...
Calc-You-Later's user avatar
13 votes

What will succeed the Arecibo Observatory?

The big loss is to radar astronomy. Arecibo was one of only two radar telescopes in the world in regular use, and was by far the more powerful: a 300 meter antenna and megawatt transmitter, versus ...
Mark's user avatar
  • 3,103
13 votes

How are radio telescopes pointed?

There are several ways to point a radio telescope. Some radio telescopes are mounted with an optical telescope pointed in the same direction. The user moves the optical and radio telescopes together ...
Connor Garcia's user avatar
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12 votes
Accepted

Why the blank wedges in this very early 21 cm map of the Milky Way? (Oort et al. 1958)

TLDR: these wedges are bits where things are moving around the centre of the galaxy at about the same speed as us, so we can't understand what is there. As it states on page 4 of the paper you have ...
FJC's user avatar
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12 votes
Accepted

Why does the author believe that the central mass that gas cloud HCN-0.009-0.044 orbits is smaller than our solar system?

The authors were able to successfully model the motion of the gas streams as Keplerian orbits around an object of $\sim30000M_{\odot}$. In doing so, they derived some key quantities, such as the ...
HDE 226868's user avatar
  • 36.3k
12 votes

How did Arecibo detect methane lakes on Titan, and image Saturn's rings?

It did not detect methane lakes. It found that Titan was shiny (in radar terms): that is, the reflections were from a smooth surface rather than a rough one, and at the same time not very intense. ...
Martin Kochanski's user avatar
12 votes

Has radio astronomy ever been done on objects that appear very close to the Moon? Is this avoided?

Occulations of artificial probes has been used to investigate the ionosphere of the moon. See, for example http://adsabs.harvard.edu/full/2008MSAIS..12...53P In this technique, radio signals from the ...
James K's user avatar
  • 118k
11 votes
Accepted

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. ...
Lee J Rickard's user avatar
11 votes

How to know that the 21cm Hydrogen line is the actual emission and not any other redshifted line?

No, not really. The first thing is that we know that ${H}$ is far more abundant than other elements or simple molecules in the universe. The next thing is that the 21 cm line comes from a ...
Carl Witthoft's user avatar
11 votes

Why does the Event Horizon Telescope (EHT) not include telescopes from Africa, Asia or Australia?

Would it increase the diameter if they would include some from there? No. Not by much, at least. The telescopes are already ~20,000 km apart, so you can't create a longer baseline that still has a ...
Hobbes's user avatar
  • 3,034
11 votes

Artificial radio waves masked by a star's natural radio waves?

The Sun emits incoherent radio signals over the full range of frequencies. The signals are not modulated in any meaningful way. Humanity emits signals at particular frequencies that are then modulated ...
ProfRob's user avatar
  • 149k
10 votes
Accepted

What exactly is interplanetary scintillation; what was the Interplanetary Scintillation Array looking for? Did it successfully observe any?

To fully answer your questions, let me introduce scintillation before interplanetary scintillation. Atmospheric scintillation The imaging of an astronomical source is affected by a collection of ...
NGsp's user avatar
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