# Tag Info

36

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 and collaborations. Unless someone was to build an identical observatory at the same latitude as Arecibo, with the same frequency range, receiver options and ...

36

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-array or other composite system, because the beam pattern is a simple Airy disk rather than a complicated pattern formed by tens or hundreds of such disks.

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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 magnetic field produce beams of radio waves that sweep past earth every 10 hours. These are detectable in the amateur range, at about 20 MHz. Nasa make a kit ...

25

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 expensive, not less. Otherwise that is what people would have done in the past. Arrays are built because you can synthesize a larger diameter of aperture. In ...

24

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 2003 DOI: 10.1126/science.1088969 This was a really elegant experiment! A continuous, unmodulated, circularly polarized 13 cm wave was broadcast from Arecibo ...

23

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 $$1\text{ Jansky}=10^{-26}\text{ Watts meters}^{-2}\text{ Hertz}^{-1}$$ One hertz is one cycle per second, which makes me suspect that the "c" stands for cycle. It might seem curious that the authors choose to ...

21

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 filtering was done to all the maps in the paper and will be responsible for the dramatic "hole" in your Fourier transform. As for the high frequency ...

19

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: $((1 + (kx/5)^{-4})^{-1}) * ((1 + (k/150)^{-4})^{-1})$. This second filter gives the "hole" and a "thin" vertical line in your 2D PS. The image above is just for PR purposes. In ...

18

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 273. Scheuer 1965 goes into a little bit of detail on general computations. A slightly different tack was taken by Vedantham et al. 2015. They were attempting to ...

18

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 need extremely large arrays to compensate for this. Granted, such arrays are certainly possible (ignoring the fairly sizable cost cost), as demonstrated by the ...

14

@Arne is right in his answer about two things, that the most suitable frequency for Jovian amateur radio is 20.1 MHz, and that this is a 15 meter wavelength. However, the antenna can actually be half the wavelength, and amateur radio astronomers have had good results listening to all kinds of Jovian sounds, including detecting occultations of its many moons ...

13

Interesting idea. I think the answer is both yes and no -- yes with a manufactured dish but no in the crater's raw state. The Arecibo telescope sits in a natural crater, but adds a dish which has a couple of important things required by a radio dish: a radio-reflective surface a specific curvature, classically parabolic, but also shaped low surface ...

13

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 paper names bremsstrahlung, gyroresonance, cyclotronmaser, and plasma radiation as sources, each with their own brightness temperature way above 6000 K. (See also ...

13

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 still is quite a widely-used radio observatory. It helps in many initiatives, not limited to but including Breakthrough Listen. I know there are many people who ...

12

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, usually taken to mean their standard deviation. If you measure the velocity of several light sources (from the Doppler shift of their spectral lines) that are ...

12

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 interferometer made from two 1m satellite dishes available. All these dishes can be used to do interesting things, but you'll need to match the instrument to your ...

12

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. As a result (quoting the 2003 New Scientist article Radar reveals Titan's methane lakes linked in one of the comments to your question), “some researchers ...

12

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 probe are monitored as the probe passes behind the moon. There is refraction from the lunar ionosphere, which can be detected indirectly, using a doppler ...

12

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 Goldstone's 70-meter antenna and 500-kilowatt transmitter. I'm not aware of any plans for successors: FAST can't be fitted with a transmitter without a complete ...

12

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 receivers very exactly aligned. For example, Arecibo's Gregorian dome could be aligned with any location on the order of millimeters, while the Green Bank Telescope's ...

12

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 shorter wavelengths, and so visible light from the Sun scatters much more than radio waves from the Sun.$^{\dagger}$ The former effectively fills the daytime sky, ...

11

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 pericentric distances of these two gas components (the "Balloon" and the "Stream"). One has its closest approach at $\sim0.21$ pc; the other has its closest approach ...

10

They're not different. Same principles do apply. You could have secondary, tertiary, quaternary, and so on, mirrors with instruments at any wavelength, either optical, or radio, or infrared, etc. You could also have instrumentation placed directly in prime focus (so no mirrors other than the primary) with any kind of instrument - radio or infrared or visible ...

10

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 target needs to be within the isoplanatic angle of a bright enough references star. (Even with laser guide stars, there is still a need for a reference star for "...

10

As others have noted, you will not be able to detect a star using an oscilloscope and an antenna. The received signal level is too low, and the oscilloscope not nearly sensitive enough. A radio telescope consists of an antenna, an amplifier, and a receiver (that incorporates other amplifiers and other stuff besides - like filters and mixers to select the ...

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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 simultaneous view of the target. Don't forget: Earth is a sphere. Only one half of that sphere can observe M87 at the same time. Telescopes in the Eastern ...

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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 effects that goes under the name of astronomical seeing, the main ones being smearing, motion and scintillation of the image. All these effects are caused by the ...

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Radio astronomy involves a wide range of frequencies, covering the range from $\sim$10 MHZ to $\sim$100 GHz.$^{\dagger}$ With four orders of magnitude to work with, the most valuable band depends strongly on what sort of object you're observing, as well as what receivers are actually available on a specific telescope. Given the diversity of sources out there,...

9

An earlier paper on the object (Oka et al. (2015)) explains that CO-0.40-0.22 is a "high-velocity compact cloud". The first discovery of such an object was two decades ago (Oka et al. (1998)), when CO 0.02-0.02 was found. The naming convention used for that object was "CO" + Galactic longitude + Galactic latitude For instance, CO 0.02-0....

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