# Tag Info

29

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 ...

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 ...

23

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 ...

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 ...

13

@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 ...

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

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 ...

11

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 ...

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 ...

10

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 ...

10

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 ...

9

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 linked, the great gap between 315 and 340, where, except at small R, the differential rotation is too small to separate the various arms The method used ...

9

"Peculiar velocity" is a fixed term and describes the velocity of an object relative to a defined rest frame. Astronomy has the problem that you need different methods to measure the 3D motion of an object. Therefor one often only gives the velocity within line-of-sight (from spectrographic data) or the perpendicular velocity as measured from ...

8

The first thing to consider is that the area of a beam will, over long distances, diffuse. The best situation we can hope for is a diffraction-limited system, where this diffusion is minimized thus maximizing our received signal. That is, in theory we have a perfectly collimated transmission beam that neither diverges nor converges. In practice, we are ...

8

All electromagnetic radiation from a point source - which a normal radio transmitter is - propagates according to the inverse square law which means that the intensity of the signal is inversely proportional to the square of the distance. This happens on earth and in deep space equally. So this will mean that for any signal there will be a distance at which ...

8

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 Alike 4.0 License. The majority are space-based, although the radio telescopes are largely land-based. They cover existing and future telescopes, at energies ...

8

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....

8

From "The 10.7 cm solar radio flux ($F_{10.7}$)", It has become clear that wavelengths in the region of 10 cm are best for monitoring the level of solar activity because solar emissions at these wavelengths are very sensitive to conditions in the upper chromo- sphere and at the base of the corona. This is not saying that exactly 10 cm wavelength ...

7

I'm not an expert in this, but it's a fun little blip in the history of SETI. Pretty much the only blip I think. I understand the incredibly high signal strength it entails. I wouldn't call it "incredibly high". It peaked at 30 times normal. source, and that's inside the "waterhole" a frequency range where the background radiation is the lowest in the ...

7

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. In those cases, they are usually being used to correct for the artificial structure introduced by the way the interferometer samples the sky, rather than for ...

7

Using current technology (and by that I mean experiments and telescopes that are available now) we would probably be unable to detect life on Earth even if observed from a distance of 4 light years, which is the distance to Proxima Centauri. A "blind" search could look for radio signatures and of course this is what SETI has been doing for lots of ...

7

The Intergalactic medium at the relevant redshift is made of neutral hydrogen. What we can measure is the brightness temperature (the temperature that the IGM would have if it emitted as a blackbody) relative to the CMB. This quantity depends crucially on the following expression: $\frac{T_S - T_{CMB}}{T_S}$ where $T_S$ is called spin temperature. The ...

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