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Questions tagged [radio-astronomy]

Questions about observation performed in the radio frequency range of the electromagnetic spectrum (between 10 MHz and 1GHz).

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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 ...
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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 ...
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1answer
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Could the E.H.T. produce an image of the human artifacts on the moon?

Two days ago the New York Times featured the Event Horizon Telescope (E.H.T.), a huge virtual radio telescope emerging from combining data from several dishes scattered around the world. While the E.H....
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1answer
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Units in optical and radio spectral data cubes: Flux vs Brightness

I have noticed that the units used in spectral data cubes coming from optical IFU instruments are usually in $erg/s/cm^2/Ang/pixel$. To my understanding this is a measure of Flux. Right? However, in ...
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1answer
115 views

Is it possible to define a state of zero absolute angular momentum anywhere in the universe?

Conservation of angular momentum doesn't seem correct to me. I think this because radiation is present everywhere, no space is completely void, and no object perfect. Thus all objects will have uneven ...
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1answer
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Converting Jy/beam to Jy?

Maybe its a dumb question, but to convert Jy/beam to Jy, I just have to multiply it by the beam size in sr right? Being $\Omega$ the beam size: $\Omega = \frac{\pi \theta_{maj} ~~ \theta_{min}}{4 \...
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Hydrogen Line observation - Interference from trees

I am setting up a 2.4 metre parabola pointing straight up to observe the 21cm hydrogen line at 1420MHz with meridian drift scans. I'm planning to place the dish on a steel pole embedded in the ...
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1answer
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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 ...
2
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1answer
57 views

Different radio process band ranges

If we want to observe a galaxy for which we have optical data, what parameters we need to know to calculate its total radio flux at 3 cm? Specially I am interested to know how to differentiate among ...
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Amateur radioastronomy: dish suggestions

What kind of amateur radioastronomy can any interested citized do with: a) A 2 m dish antenna. b) A 2,5 m antenna. c) A 3 m antenna. d) A 5 m antenna. e) A >5 m <10 m antenna (likely I can not ...
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Strange behaviour of black holes [duplicate]

We know black holes emit streams of radiation ,also recently discovered that they emit visible light when they eat any nearby matter . "We find that activity in the vicinity of a black hole ...
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How to analyse Jovian signal received at 20.1 MHz using dual dipole antenna? [closed]

I have purchased a Radio Jove kit and set it up. I have also received some signals. I am using Radio Skypipe II software as discussed in this Radio Jove tutorial (see also here) with a sound card to ...
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2answers
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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 ...
6
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1answer
246 views

Early universe's first starlight (indirectly) detected for the first time, could it have been detectable with 1970's technology?

The recent paper in Nature An absorption profile centred at 78 megahertz in the sky-averaged spectrum seems (to me at least) to be an incredibly simple and elegant experiment with far-reaching ...
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How to measure uncertainty in flux density?

Let's say I have an image of a galaxy that is 10 pixels, and the pixels have values 1, 2, ... 10 Jy/beam. If the RMS background noise is 1.5 Jy/beam, and I want source detection at 3 sigma level (...
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Nature and mechanism of the short-term variability in radio strength of Sgr A*?

The Phys.org article Cosmic filament probes our galaxy's giant black hole links to A Nonthermal Radio Filament Connected to the Galactic Black Hole? which discusses (among other things) the importance ...
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1answer
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Is there a complete edition of the Cambridge Catalogue of Radio Sources (esp. 3C) available digitally?

In radio astronomy, many common objects are refered to by their designation from the 3rd Cambridge Catalogue of Radio Sources, e.g. 3C 353. For hobbyist purposes, I would like to create a catalogue ...
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Why does the transition frequency of an ensemble of synchrotron electrons depend on the angular size of the radio source?

The synchrotron spectrum from a power-law ensemble of electrons in a uniform magnetic field, $B$, looks like this. In "The Physics of Extragalactic Radio Sources" by De Young it says, "The overall ...
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2answers
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How to calculate the integrated source flux density of a continuous source?

I'm working with data from radio surveys. My images are .fits files with BUNIT Jy/beam. I want to calculate the net flux from a continuous source (not point source). When I simply added all the ...
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1answer
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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 ...
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1answer
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How to know that the 21cm Hydrogen line is the actual emission and not any other redshifted line?

Is it possible that we mistake some other wavelength emission to be 21 cm because of redshift?
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How large does refraction become in radioastronomy?

For atmospheric refraction of visible light, Wikipedia gives the order of 1 arc minute at 45° altitude above the horizon, and 5.3 arc minutes at 10°. This is caused by the dielectric polarizability of ...
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1answer
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What is the extent of the “worldwide campaign” to observe near-earth object 2012 TC4?

This nifty answer describes and provides links to the data of the recovery of near earth object 2012 TC4, and the answer also shows the first actual image of the body for this pass. At apparent ...
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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 ...
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1answer
99 views

“Mysterious radio signals” - how could a geostationary satellite and Ross-128 line up with Arecibo?

The Phys.org article 'Mystery' signal from space is solved. It's not aliens cites a summary of the conclusion "by Abel Mendez, director of the Planetary Habitability Laboratory at the University of ...
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1answer
106 views

What are infall signatures in stars?

I came across several papers (e.g. Looking for outflow and infall signatures in high mass star forming regions P. D. Klaassen, L. Testi and H. Beuther, 2011) talking about infall signatures in star ...
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1answer
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The M-theory to understand black holes [closed]

I am a layman in astronomy. Can someone please explain it to me whether the M-theory can be used to explain what is happening in the centre of the black hole where the singularity exists? Or is it ...
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1answer
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How do ASKAP's focal plane phased array feeds interact with the entire array phasing?

Sky & Telescope's ASKAP Joins the Hunt for Mysterious Bursts says: A new telescope, the Australian Square Kilometre Array Pathfinder (ASKAP), has joined the search for energetic and elusive ...
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2answers
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How to find period of a pulsar from a given time sampled voltage data?

I've a data file with 2 columns, each containing time sampled voltage output (a sequence of real numbers) from a radio telescope, so there is a pair of telescope which are measuring the signal here. ...
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2answers
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Has the microwave background radiation ever been blocked in order to prove it's really from the sky?

A rather stupid question but I was just curious if the radiation could be virtual. From the instrument....sort of like virtual particles. In other words if you just build a sensitive microwave ...
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1answer
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Help with homwork - Astronomy

We might expect to not find life around halo stars (“Population II” stars) because: a) they are out of the plane of the galaxy and thus exposed to more cosmic rays (energetic nuclei) b) these stars ...
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How was Sugar Grove Station supposed to work?

Sugar Grove Station was an outpost designed to listen in on Soviet radio signals reflected off the moon. How would this work? Wouldn't the radio signals be distorted by the imperfect surface of the ...
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Radiometer Equation for Flux Density

In Duncan and Lorimer's Handbook of Pulsar Astronomy, the equation for the flux density using a radio telescope is given as (for a top-hat function): $$S=\frac{\beta\,\mathrm{SNR}\, T_{sys}}{G\sqrt{...
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1answer
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Why do Seyfert Galaxies emit less energy than Quasars and Blazars, and how is the emitted energy measured?

When I was reading information about QSOs on a website, it said that Seyfert Galaxies emit less energy than Quasars and QSOs. Why do Seyfert Galaxies emit less energy than quasars, and how is this ...
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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 ...
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How does the Event Horizon Telescope implement the interferometry?

The BBC article Event Horizon Telescope ready to image black hole describes the Event Horizon Telescope, a coordinated observing technique with several radio telescope arrays across the globe forming ...
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Is “Giga-hertz Astrophysical Transient Emission” distinct in any way from “Fast Radio Burst”?

In this answer I have just read about The University of Texas Rio Grande Valley's The Spacecraft Tracking and Astronomical Research into Giga-hertz Astrophysical Transient Emission (STARGATE). While ...
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1answer
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Why levels of radio contours maps are given in mJy/beam and what does it mean?

I know what a jansky is, but don't understand "/beam". If jansky is a unit of flux density, what kind of unit is Jy/beam?
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How do astronomers at SETI know if they received intelligent radio signals from other planets?

Do they expect to see wave modulations like the ones we use in our technology? what do they expect the waves to be like exactly?
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What does the velocity dispersion of a galaxy mean?

Also, what is the advantage of getting information about the velocity dispersion of a galaxy?
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Astronomy online degrees

I have a masters degree in computer science and statistics but would like to advance my knowledge in astronomy, ideally in getting some kind of online degree. Does anybody have experience, ...
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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 ...
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1answer
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Why does the neutral hydrogen velocity have this characteristic behavior in the galactic plane?

The recently released map of galactic neutral hydrogen density and velocity is really beautiful. The work has been relased by the HI4PI collaboration (HI = neutral hydrogen, $4\pi$ = complete ...
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What is precipitable water vapor in millimeter-wave radioastronomy and how is it measured?

Looking through ALMA on-line documentation and articles, the quantity PWV (precipitable water vapor) is a central theme. I have two linked questions. What (actually) is precipitable water vapor, and ...
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1answer
177 views

Cosmic microwave background radiation: why did it take so long to get here?

I understand that the universe after the big bang was a super dense cloud of elementary particles, and because of this high density was "not transparent" to light. Then, roughly 400.000 years (380....
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1answer
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What are the Similarities and Differences between ALMA and FAST?

What are the Similarities and Differences between ALMA (Atacama Large Millimeter Array) and FAST (Five hundred meter aperture spherical telescope)? What can they see, what's their resolution like? ...
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Astronomy & machine learning. Where to start? [closed]

I am a Computer Engineering major and would like to learn more about machine learning methods in Astronomy. What books or other resources could I use?
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1answer
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Is radar interferometry used, or feasible, for ground based astronomy?

I've heard of "interferometric synthetic aperture radar" being used for Earth observation from satellites and airplanes. Is active radar used interferometrically for astronomical purposes too? Such as ...
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Can all astronomical signals be considered Gaussian noise?

While studying the techniques astronomers use to mitigate radio frequency interference (RFI) I found it's often assumed that astronomical signals are (band-limited) Gaussian noise. Is this a ...
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Can radio telescopes such as arecibo image the subsurface of asteroids or planets?

This was done with the moon: Radio Dishes Peer Beneath Moon's Surface