Hot answers tagged

11

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 ...


10

@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 ...


7

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 ...


6

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 ...


5

Since the astronomers are using radio telescopes and not optical telescopes, I'd like to point out why they are doing so - The centre of the Milky Way is a very dusty place. Wavelengths from the millimeter to optical get easily absorbed by all this dust, so it's very difficult to see the centre of the galaxy in the optical spectrum. But radio waves do not ...


5

The StarGazers lounge featured a radio kit article for Jupiter radio astronomy. The same article is also featured over at the Radio Group of BritAstro. It seems that 20.1 MHz is the suitable frequency for amateurs observing Jupiter. I am far from being an expert for radio astronomy, but for a small source such as Jupiter, I would assume that you need a big ...


5

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 ...


5

The relation you cited holds for a single telescope. But, as also noted in the lecture you linked "One thing that is possible in radio astronomy is to use interferometry, which combines the signals from an array of antennas as if they were all part of the same aperture. That means that the resolving power of a radio telescope is not just what it would be ...


5

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 ...


4

A parabola does indeed focus over a broad frequency range. The lower limit is determined by the dish diameter, the upper by the construction (mesh size, parabolic accuracy etc.). The collector placed at the focal point may be a simple dipole or other fixed frequency antenna, or more commonly, a waveguide that leads the collected signals to a low noise ...


4

The resolution/error box. Radioastronomy has always been hindered by the resolution, because it is inversely proportional to the size of the telescope and making larger telescopes (even with interferometry) is not always easy. No amount of modern technology can substitute for a large effective diameter. (When I say effective I'm including interferometry ...


4

From my simplistic analysis, it's not good for much. For comparison, the first radio telescope was 9 meters. One of the favorite parts of the spectrum for radio telescopes is the water hole - 21 cm. From my quick mental arithmetic, this dish would be able to resolve sources of 21 cm signals of they were about 5 degrees apart. I'll update with links and ...


4

It's just as simple as taking the flux at some wavelength (just a number) and using this number to represent a visible intensity. If you only have one wavelength then you can only get a monochrome picture. However, if you have flux information at more than one wavelength, let's say three, you can use the flux at the longest wavelength to represent red (r), ...


3

Could large craters on the moon be used as reflective lenses for radio signals? You'd have to line the surface with something reflective to microwaves, like a metallic mesh, or similar materials. Secondly, the shape of the crater is probably not quite ideal, so it would have to be adjusted a little, carved up a bit in various places. But it's a good ...


3

The first thing to notice is that the Local Interstellar Cloud, in which the Sun is evolving right now, is a fairly diffuse region, with a typical density of about one to a few particles per cubic centimeters. Clouds with such low density are actually mostly atomic; as you can see on this plot (Snow & McCall 2006, adapted from Neufeld et al. 2005): It ...


3

I think the image you posted is not quite reallistic. On it, objects are just inverted from some radius on, while what you can expect from a real black hole seen from near enough is a combination of these: a) an accretion disc b) a companion being sucked c) Hawking's radiation d) X-Ray burst from the poles (really starting out of the event horizon) You ...


3

If you look at raw resolving power you get for a 10m optical telescope: $\theta_{optical}\approx \frac{5\times 10^{-7}}{10}\approx 5 \times 10^{-8}$ radian. For a synthetic aperture ground based radio telescope operating at 21cm the limiting aperture is of the order of the diameter of the Earth so: $\theta_{21cm}\approx \frac{21\times 10^{-2}}{12\times ...


3

Rather than looking for ready-made systems, take a look at projects. Right now, plenty of amateurs are using software defined radio coupled to various antennas for astronomy. Start here: http://www.rtl-sdr.com/rtl-sdr-for-budget-radio-astronomy/ And while it has nothing to do with imaging, there's plenty of radio astronomy that amateurs can do using simple ...


3

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 ...


2

1MW of transmitted power is very modest by RADAR terms, to give one example. Thus, you probably need to establish what exactly your professor means by "brightest" (may it be a specific wavelength or point in time, or some other definition). Otherwise, there's no reason to believe that Arecibo transmission was any special or outstanding from radio engineering ...


2

It cannot be said correctly, since we humans have hardly traveled to the moon and sent space probes to explore other planets in our solar system. So, theoretically anything might be possible. I'm trying to be a bit practical here. The only man made object that has gone really far is Voyager 1, which is at a distance of 18.7 billion kilometers (125.3 AU) from ...


2

Tired light has been used as an explanation before, whereby light loses energy whilst travelling through space---a sort of drag effect. I don't think anyone actually supports it nowadays, though.


2

The pointing is not a fundamental problem with the suggested design: The suggested trajectory is designed to include a Sun flyby as the last flyby. This ensures an asymptotically radial trajectory away from the sun after the flyby, hence maintaining the pointing relative to the sun. The proper motion of the observed object may be some challenge, but the ...


2

2SB is Dual Sideband, as opposed to DSB - Double Sideband. Here are a couple of papers you might find relevant and interesting: a 2SB upgrade replacing a DSB a paper that mentions the advantages of 2SB over DSB


2

Take for instance radio, when listening to radio you gather static on the frequency. A passband filters the static which in turn provides a clearer signal. Objects radiate in multiple frequencies/wavelengths, for instance heat/thermal (infrared) and visible. Not all object radiate in a range of frequencies, humans for example can be seen well in infrared and ...


2

LOFAR does not go 'through the ionosphere' as it's ground based. Rather, it is able to receive signals from outside the ionosphere due to the very low frequencies involved. These frequencies (naturally) have very long wavelengths, which means that LOFAR must be very large to obtain a decent level of resolution. The number of antennae will affect sensitivity ...


2

If it works for Arecibo it could be made to work on the moon. Ceres, and maybe even Mars. The point about sending a prefab is a good one. And using two radio telescopes in tandem separated in space would allow for astronomers to take advantage of the improved angular resolution this affords provided they were arranged so as to allow them to simultaneously ...


2

Radio telescopes are frequently used to observe the births of stars and their planetary systems. The longer wavelengths are able to penetrate from beneath the envelope of gas and dust that shrouds any attempts to view these events at optical or infrared wavelengths. Unfortunately, the smallest angular resolution of a telescope goes as $\lambda/D$, where $D$ ...


2

There are tons a amateur radio astronomy clubs and groups. Radio Astronomy was basically started by an amateur named Grote Reber, where he basically did the experiment that you are pondering to do in 1937 in his backyard in Wheaton, Illinois. You can visit that exact instrument at the NRAO facility in Green Bank, West Virginia. It was named a National ...


2

Well, that might depend on exactly what definitions you use. SETI itself is a broad program. In this answer I'll focus solely on what I consider the most iconic part of modern SETI, which is SETI@home. We have the following quote from SETI@home's webpage (emphasis their own): SETI (Search for Extraterrestrial Intelligence) is a scientific area whose ...



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