# Tag Info

35

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.

33

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 ...

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 ...

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 ...

16

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 ...

12

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 ...

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

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 ...

9

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 ...

7

Connecting an antenna directly to oscilloscope will not give reception, even with a strong radio source. First problem is the power level. Typical received power from antenna would be around -100 dBm, i.e. $10^{-10}\,\textrm{mW}$. A typical oscilloscope has an input impedance of 1 Mohm, which means if all the received power went there, it would give a ...

6

The size of your dish determines two things: Along with the temperature of your electronics, determines the signal-to-noise ratio of your telescope. The size of your dish determines the angular resolution you can expect. This has an approximate relationship of $$R = \lambda / D$$ where $R$ is your angular resolution, $\lambda$ is your wavelength of light ...

6

Why does the Event Horizon Telescope (EHT) not include telescopes from Africa, Asia or Australia? Why were not they included? Africa doesn't have a radio telescope in the frequency range necessary (230-450GHz) to participate in the EHT array. For Asia Wikipedia lists the "Yevpatoria RT-70 radio telescope" as capable up to 300 GHz and located in western ...

6

The Nature paper by Bertoldi et al. (2006) says: Our millimetre observations were performed with the Max-Planck Millimeter Bolometer (MAMBO-2) array detector at the IRAM 30 m telescope on Pico Veleta, Spain. This is a ground-based telescope in the Spanish Sierra Nevada mountains at 2850m to try and get above as much of the precipitable water vapor, which ...

6

Coherent interfering signals are usually referred to as RFI (or Radio Frequency Interference). One could certainly digitally filter out a coherent interfering signal from a telescope by observing from an additional telescope focused on the source of the interfering signal, given the proper geometry. Here is a research paper on Radio Frequency Interference ...

5

I'm not sure what you mean by "wave modulations". Loosely speaking, there's 2 things to look for regarding alien intelligence/technology. One is a signal of some kind and the other is a very large or very energetic structure. The most obvious place to look for a signal is in the water-hole. Good article on that here. Because of the relatively low ...

5

That's the Very Large Array. The very large array is a Y shaped array of massive Radio astronomy observatory. It has the computing power to function as an interferometer. Each radio is mounted on double parallel railroad tracks, so the radius and density of the array can be transformed to adjust the balance between its angular resolution and its surface ...

5

ALMA produces stable, mutually coherent ~THz LO (Local Oscillators) for all the antennas by... Using a single central LO and piping it to every antenna via fiberoptic cable! The fiber expands and contracts due to temperature fluctuations so a laser system is used for calibration among the antenna. If you can believe it, they manually lengthen or shorten ...

5

What part of the EM spectrum was used in the black hole image?... Is it an image in visible light, infra-red or longer? Microwaves, (millimeter waves actually), and the hairy edge of far-infrared at a nominal frequency of 230 GHz or 1.30 mm wavelength, the bandwidth is roughly 2 to 6 GHz wide depending on how many channels of data were used to produce the ...

5

tl;dr: @Hobbes' answer is demonstrably wrong; the EHT takes a large fraction of its data when the target is not visible from one of the extreme sites. If there were sites distributed all the way around the earth, it would be tremendously advantageous to collect from all of them, and the image resolution would improve with the addition of longer duration ...

4

They scan the object, if you point the dish a a point in the sky as the Earth rotates the dish scans across astronomical objects, then move the dish to point at a slightly different position and let it scan across the object again, and again. After a while you can re-construct an image from the scan lines in a similar way to analogue TV.

4

Large radio telescope have pretty good pointing accuracy: the individual dishes of the VLA are accurate to about 10 arcsec. the giant Lovell telescope at Jodrell Bank has a similar accuracy. The second critical parameter is the beam width. Beam width depends highly on frequency: beamwidth = wave length/dish diameter When you use several dishes in an ...

4

It is wasteful to sample with many bits because the signal to noise ratio at the ADC of a radio telescope is typically << 1, so using many bits would just be resolving noise. (An exception to this is when there is strong radio-frequency interference that needs to be resolved, but this is not a big problem for ALMA due to its location and observing ...

4

It is important to understand how this process works. The method described in your article is known as Bistatic Radar. In effect, a transmitter sends out a signal (generally a radio telescope in the microwave region) which hits the surface of some body and bounces off to be received back on Earth by a second, separate radio telescope. Now, because a ...

4

I have a used 2.4 metre mesh C band dish that I picked up for free that I will be converting for observing the 21cm hydrogen line @ 1420MHz. I was lucky with this dish as it's in as new condition, but you need to be aware of any rusting and damage to the mesh that will distort your data. I'm mounting mine in my backyard on a 75mm steel pole 2 metres above ...

4

You are right that the image is not a visible light image. It was taken using very, very short wavelength microwaves -- the wavelength is 1.3 mm which is only a bit shorter than the Far IR! I think you may be reading a bit too much into the word "photo" which, as you say, has the everyday meaning of "taken with a camera using lenses in visible light." I ...

4

How do radio telescopes gather information about visible light? They don't; the picture you saw all over the news was a false color image, where frequencies are shifted from the radio spectrum to the visible spectrum (blue meaning shorter radio wavelengths and red meaning longer radio wavelengths) and/or the intensities mapped to different colors (instead ...

4

tl;dr: The less complicated you want to make your dish, the closer to the equator you want to put it. Since you are asking about single craters I assume this question is about using a crater as a natural pre-form for a single, large dish antenna like Arecibo Observatory and FAST. On the Moon with no atmosphere or ionosphere nearly the whole sky is available ...

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