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Questions tagged [radio-astronomy]

Questions about observations performed in the radio frequency range of the electromagnetic spectrum.

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

It seems that most of the modern radio astronomy instruments and observations that make the news are interferometers or phased array systems of one kind of another. Is there any application left for ...
Steve Linton's user avatar
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37 votes
3 answers
2k views

If Alpha Centauri A's solar system exactly mirrored our own, what would we be able to detect?

Suppose there was an exact replica of our solar system 4.4 ly away (people included). What would we be able to detect and with what telescope(s)? Which planets? Could we detect radio transmissions and/...
Nick T's user avatar
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33 votes
4 answers
3k views

What will succeed the Arecibo Observatory?

Just a few minutes ago, I got a notification from Space.com stating that the Arecibo Observatory will be, sadly, decommissioned due to extensive damage to its structure. So, with the loss of one of ...
WarpPrime's user avatar
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20 votes
1 answer
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"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?

In Nature News' August 11, 2023 Closing down an icon: will Arecibo Observatory ever do science again? found in The Observatory there is discussion of the Next Generation Arecibo Telescope (NGAT): ...
uhoh's user avatar
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19 votes
3 answers
3k views

Can I sense a bright star pointing an eight foot antenna towards it?

If I connect an eight foot Yagi or other comparable sized antenna to my oscilloscope and point the antenna at a bright star will I see a voltage on my oscilloscope? I am not interested in turning the ...
Lambda's user avatar
  • 514
19 votes
5 answers
3k views

Can impact craters on the moon act like giant radio telescopes?

Could large craters on the moon be used as reflective lenses for radio signals? Acting like a large radio telescope reflecting radio waves to a satellite positioned over the crater.
Reactgular's user avatar
18 votes
4 answers
7k views

Jupiter FM - What are practical and inexpensive ways for the amateur detection of signals from Jupiter, especially of the transit of her moons?

What modifications to a standard AM/FM or shortwave radio are needed in order to be able to detect radio-wave signals emitted from Jupiter? Would it be possible to detect the transit of the major ...
user avatar
18 votes
2 answers
1k views

What are practical considerations for backyard radio-astronomy detection of black holes?

Evidently, direct observation of a black hole for an amateur astronomer, such as described for what professionals do in the question "How are black holes found?" would be nigh on impossible, so the ...
user avatar
17 votes
2 answers
4k views

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

The BBC's Desert telescope takes aim at ageing our Universe contains the image below of the Cosmic Microwave Background from the Atacama Cosmology Telescope or ACT. It looks like this is plotted with ...
uhoh's user avatar
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15 votes
2 answers
3k views

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

This answer to Which kinds of astronomical observations most need to avoid the Moon being up? mentions For completeness - radio, mid-infrared and mm-wave observations are unaffected (unless the ...
uhoh's user avatar
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14 votes
1 answer
463 views

How do radio astronomers avoid having their receivers burned out by ground-imaging radar from satellites?

After about 34:00 in the 9th press conference of AAS 235, radio astronomer and NRAO's spectrum manager Harvey Liszt talks about Radio Astronomy in a New Era of ...
uhoh's user avatar
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13 votes
3 answers
2k views

How are radio telescopes pointed?

In the past, I worked as a programmer in a radio astronomy station, and since then I have a question on my mind. To observe a star with a telescope, we locate its location with our eyes and then we ...
Aminos's user avatar
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13 votes
2 answers
254 views

Why hasn't VLBI been used to try and image giant exoplanets?

A Jupiter-sized object at 10 pc subtends an angle of 0.0001 arcseconds (100 micro-arcsec) at the Earth. The Event Horizon Telescope interferometry network is capable of a (demonstrated) angular ...
ProfRob's user avatar
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13 votes
1 answer
153 views

How can maser emission be unpolarized?

I was reading that: However, unlike Galactic sources such as W3(OH), the emission is unpolarized and the 1667 MHz line is stronger than the 1665 MHz line. but how is this possible? Does not the ...
Mathews24's user avatar
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12 votes
2 answers
3k views

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

This answer to Farthest distance to a solar system object that's been measured by radar? mentions that Saturn's rings, and the Uncover Travel post Arecibo Observatory, Puerto Rico – The World’s ...
uhoh's user avatar
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12 votes
2 answers
899 views

Why aren't ground-based observatories using adaptive optics for visible wavelengths (circa 2016)?

Adaptive Optics (AO) techniques allow ground based observatories to dramatically improve resolution by actively compensating for the effects of Astronomical Seeing. The atmospheric effects are quite ...
uhoh's user avatar
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12 votes
3 answers
422 views

What else could the Event Horizon Telescope Observe?

The Event Horizon Telescope was made possible in order to observe the details of supermassive black holes. This took a huge amount of work installing extra telescopes and developing the hardware and ...
Steve Linton's user avatar
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11 votes
1 answer
2k views

A "strange" unit radio astronomy

I'm reading up on radio astronomy, and I came across this paper from 1964. At the bottom of page 193, the author uses a unit that I've not seen before in discussing radio power emission from stars: ...
Jim421616's user avatar
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11 votes
1 answer
2k views

How big a dish do I need for radio astronomy?

I've recently become interested in the idea of building my own small-scale radio telescope. A quick online search finds a few instructions on how to build this using a satellite dish. These suggest a ...
Beta Decay's user avatar
11 votes
1 answer
9k views

What does the velocity dispersion of a galaxy mean?

Also, what is the advantage of getting information about the velocity dispersion of a galaxy?
J. H. Azeez's user avatar
11 votes
1 answer
394 views

Do radio telescopes see other stars better at night?

As you know, we don’t see stars with the naked eye during the day because of the visible glare of our Sun. As I understand our Sun emits radio frequency waves, too. Is there a radio ‘glare’ from the ...
David's user avatar
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11 votes
1 answer
2k views

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

Jan Oort was a pioneer in radio astronomy. Wikipedia says: It has been written that “Oort was probably the first astronomer to realize the importance” of radio astronomy. “In the days before radio ...
uhoh's user avatar
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11 votes
2 answers
899 views

Would Adaptive Optics be Useful in Radio Astronomy?

The question Why is this video showing radio waves transmitted from a radio telescope? and this answer to it got me thinking. If atmospheric seeing at visible wavelengths is the result of refractive ...
uhoh's user avatar
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11 votes
1 answer
1k views

How can I hear (or at least detect) a pulsar at home?

Scott Manley's video Using Relativistic Raytracing &X-Rays To See Detail on Surface Of Neutron Star talks about X-ray measurements using the NICER X-ray telescope attached to the International ...
uhoh's user avatar
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10 votes
1 answer
671 views

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

Our civilisation emits radio waves into space. But insofar as the Sun can be modelled as a black body, it is also emitting radio waves into space! For an alien civilisation too far away from us to be ...
enigmaticPhysicist's user avatar
10 votes
1 answer
378 views

Can one build a distributed radio telescope?

I understand some radio telescopes are built as arrays of receivers. Could one build an array from a heterogeneous set of receivers in scattered locations? Suppose a large number of persons each ...
Joe Cooper's user avatar
9 votes
2 answers
9k views

Does the radio signal decay when it travels through the intergalactic space?

When you emit the radio signal it starts moving at the speed of light. Radio beam is diffusing with each kilometer the signal has traveled. To the nearby receiver the signal is strong. But if the ...
Kestas's user avatar
  • 163
9 votes
3 answers
2k views

Why are radio telescopes shaped so differently than optical telescopes?

Why are radio telescopes typically only a dish with a receiver above it, while optical telescopes have a primary, plus secondary and sometimes even a tertiary mirror? In other words, why do radio ...
DrZ214's user avatar
  • 1,970
9 votes
2 answers
823 views

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

Phys.org's Hiding black hole found says: A research team led by Shunya Takekawa at the National Astronomical Observatory of Japan noticed HCN-0.009-0.044, a gas cloud moving strangely near the center ...
uhoh's user avatar
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9 votes
1 answer
1k views

Why does the Sun deviate from a typical blackbody spectrum in the S band?

This is sort of a follow-up to this question, and my answer to it. The graph I see here details the radio (and other frequencies) emission of the sun. What's most notable and interesting to me is the ...
sforsingh's user avatar
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9 votes
2 answers
3k views

What kind of things I could "see" with an amateur radio telescope?

There are apparently not many reasonably priced radio telescopes available for the amateur users. I only could find a SPIDER 230C 2.3 meter diameter compact radio telescope, which costs ~10 k€. ...
mmh's user avatar
  • 394
9 votes
4 answers
831 views

Why are the ALMA receivers' ADCs only 3-bits?

above: Table 1 from Performance Highlights of the ALMA Correlators The ALMA receivers use 3-bit ADCs for what would seem to be to be a high dynamic range application needing much finer quantization ...
uhoh's user avatar
  • 30.7k
9 votes
2 answers
422 views

Do the neutrons in neutron stars emit the radio waves?

Neutrons can, especially in extreme circumstances (and large concentrations) emit electromagnetic radiation. I specifically asked about this in Physics S.E. Has a free neutron ever been shown to ...
Kurt Hikes's user avatar
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9 votes
1 answer
433 views

Why doesn't the black hole in the center of the Milky Way glow similarly to the famous M87 image?

The M87 image made some astronomers famous recently as the first image of a black hole. In the Milky Way, it has been concluded that there must be a black hole due to the movement of stars near the ...
user985366's user avatar
9 votes
1 answer
129 views

Current limitations in radio-astronomical spectrometry analysis of local interstellar cloud's hyperfine structures

I've been trying to wrap my head around capabilities of current radio-astronomical spectrometry technology to isolate not too distant tenuous sources, say, chemical composition and density of the the ...
TildalWave's user avatar
  • 6,260
8 votes
3 answers
1k views

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

The Event Horizon Telescope seems to include these radio telescopes currently: Image by European Southern Observatory (ESO)/O. Furtak; CC-BY 4.0-licensed, see the source on Wikipedia Commons and the ...
rugk's user avatar
  • 183
8 votes
3 answers
175 views

What is meant by the notation $A^{\times{B}}_{\div{C}}$; where A,B,C are real numbers?

I have come across a few papers using the notation $A^{\times{B}}_{\div{C}}$; where A,B,C are real number. For example, $3000^{\times{3}}_{\div{4}}$. An example can be Eqn (4) in Stern & Laor (...
lordparthurnaax's user avatar
8 votes
2 answers
901 views

Is Carl Sagan's famous "snowflake" quote correct?

“The total amount of energy from outside the solar system ever received by all the radio telescopes on the planet Earth is less than the energy of a single snowflake striking the ground.” ― Carl Sagan,...
ZAB's user avatar
  • 303
8 votes
1 answer
935 views

How did the object CO-0.40-0.22 get its name, and how is it distinct from CO-0.40-0.22*?

There seems to be three things described in the recent Nature Astronomy paper Millimetre-wave emission from an intermediate-mass black hole candidate in the Milky Way: Molecular cloud CO–0.40–0.22 ...
uhoh's user avatar
  • 30.7k
8 votes
1 answer
988 views

Plot of best available resolution vs wavelength - radio through gamma rays?

What I'm looking for is a graphic that shows in a general way the best available telescope resolution vs wavelength throughout the entire wavelength spectrum. So for example, there might be two very ...
uhoh's user avatar
  • 30.7k
8 votes
2 answers
751 views

What can we expect from the first accurate image of a black hole?

From recent news from the Max Planck Institute for Radio Astronomy: The European Research Council (ERC) has awarded 14 Million Euros to a team of European astrophysicists to construct the first ...
Eduardo Serra's user avatar
8 votes
1 answer
179 views

Are there any astronomical phenomena that could emit strong radio waves with multiples of a discrete frequency?

In the New Scientist article Is this ET? Mystery of strange radio bursts from space, it is reported that several times since 2001, astronomers have detected fast radio bursts that seem to have a ...
user avatar
8 votes
1 answer
1k views

Math behind a uv plot in interferometry?

I've seen standard uv plots used discussions of interferometric array designs regularly, and I have a vague idea that each arc may correspond to a pair of elements within the array, and the ...
uhoh's user avatar
  • 30.7k
8 votes
1 answer
467 views

What is a radio "homology telescope" and is the 500m dish in China one?

This question is about design aspects of large radio telescope dishes which allow them to flex under the influence of gravity as they change elevation angle, and still maintain good optical ...
uhoh's user avatar
  • 30.7k
8 votes
1 answer
255 views

Recommend a radio calibration target for amateur radio telescope

I have a small antenna and radio system that can receive frequencies between 1MHz and 1GHz. The system has a discone antenna. I plan to do some aperture synthesis based on the daily rotation of the ...
Craeft's user avatar
  • 283
8 votes
1 answer
135 views

How open is China in sharing data from the Chang'e 4 mission?

It's really good to see that man (well, machine) has gone back to the moon again. Chang'e 4 is studying potential mantle material from the lunar depths and will be conducting radio astronomy in ...
user avatar
8 votes
1 answer
431 views

Highest frequency that's been imaged by a radio telescope?

In this answer to Should we update definitions and remove the 100 GHz hard limits on radio astronomy related tags? I wrote the following partial answer: Yes, there are plenty of dishes that focus ...
uhoh's user avatar
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8 votes
1 answer
378 views

Is there a cosmic, rather than technological, upper limit to what a telescope can resolve?

Space radio interferometers could have a baseline of millions of kilometers, but is there a point where a larger baseline doesn't improve the resolution anymore because the photons observed are ...
LocalFluff's user avatar
  • 11.4k
7 votes
7 answers
1k views

Radio telescope targeting

How do you target a radio telescope on the precise object you wish to observe? You can point it in the general direction but how do you get the information from the exact point in the sky that you are ...
Nigel J's user avatar
  • 71
7 votes
2 answers
764 views

How did UV from the earliest stars 'alter the state of the 21 cm line' such that it shows up in CMB today?

In this question I discuss the recent (open access) paper in Nature An absorption profile centred at 78 megahertz in the sky-averaged spectrum at length. The abstract begins: After stars formed in ...
uhoh's user avatar
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