# Tag Info

11

You can't make an interferometer by combining photographs. You need to combine the light sources so that the light waves can "interfere", which means you need to have not only the intensity of the light, but also the phase of the wavelength. A CCD only detects the intensity. You also need to position your telescopes to sub-wavelength accuracy. For ...

9

This question amounts to: is optical interferometry possible when detecting photons? The answer to this is yes. Many experiments have been done using interferometers where one photon at a time is passed through the apparatus and still reveals an interference pattern when detected on the other side. The problems with optical interferometry are manifold: ...

8

The LIGO interferometer uses a homodyne detection technique. Basically, the light travelling in each arm of the interferometer is derived from the same laser source and is combined in the output channel and falls onto a photodiode. The interferometer is operated so that when there is no gravitational wave (GW) passing through the instrument, the beams ...

8

This link gives you all the papers that have cited the instrument description paper. The list of papers shows that it has been used for studying: the centres of AGN, close binary systems, discs around young stars, the atmospheres of AGB stars and interferometric imaging of exoplanets at least. Here is a paragraph from the instrument description paper ...

7

Radio interferometry can combine observations over very large baselines. But optical interferometry cannot. According to a list of interferometry instruments on wikipedia, the largest baseline for optical measurements is less than a kilometer. We can't take optical measurements with continent-sized instruments. Then if you drop down to radio where the ...

6

Millimeter and sub-mm observations (110-300 GHz = 2.7-1.0 mm) are sensitive to the thermal emission and provide a brightness temperature of airless bodies like the Moon or asteroids. The radio emission is from just below the surface/skin of the body (down to $\sim10\lambda$ so ~1 cm in this case) and so is also sensitive to the thermal inertia and ...

6

A 130m baseline operating at 2 microns gives a theoretical resolution of $2\times 10^{-6}/130$ radians. At a distance of 400,000 km this translates to 6m. My guess is that Genzel is referring to the accuracy with which the position of a point source of light can be measured. This not the same thing as the smallest thing you can image. The centroid of a ...

6

This is, indeed, a result of how we measure things in radio astronomy. It's not just interferometry, but radio astronomy in general. The thing they're referring to is a concept called "brightness temperature". In the low frequency limit (valid for radio astronomy), we can use the Rayleigh-Jeans approximation, which gives us the expression  T_B = \frac{...

5

Actually to convert from Jy/beam to Jy/pixel you need to divide by the beam size. Let's say you have a quantity of 1 Jy/beam, then $\frac{Jy}{beam} \frac{beam}{\Omega}$, then to go from Jy/beam to Jy/pixel you would need to divide by $\Omega$. The values of the beam major and minor axis must be in pixels. Source: NRAO

5

The basic idea behind interferometry is that of interference, the combination of two waves (in this case the electromagnetic waves from distant sources). Interference inherently implies two signals to interfere with each other, and that is why the pairs of telescopes (also referred to as baselines) are important. The interference pattern between the ...

5

When a star is occulted by a "sharp edge" such as the limb of the Moon or by an asteroid, then diffraction effects are seen. The star doesn't suddenly disappear (or appear); there are a series of maxima and minima associated with the Fresnel diffraction pattern formed by the edge. This in turn is the convolution of the diffraction pattern formed by ...

4

I asked myself the same question and back then, I found the reasoning on the German Wikipedia page pretty comprehensive. I am translating, summarizing and expanding the corresponding section in the following: By using two mirrors instead of a single one has a couple of advantages: The double telescope collects the same amount of light as an 11.8-metre ...

4

Interferometry at infrared and shorter wavelengths is more difficult than at microwave/radio wavelengths for a number of reasons. Radio signals can basically be recorded on tape (or rather hard drives these days) at different sites and then recombined (or correlated) "off-line" at another location. This won't work at optical wavelengths because of the higher ...

4

This is a really interesting question! tl;dr: A definite maybe, but you would have to engineer a clever way to focus the transmitted power to a much smaller spot first; possibly several orders of magnitude smaller than what any one dish can do. Phasing several widely-spaced dishes alone would not be enough. Let's see what can be checked easily. ...

4

Partial answer: I imagine this array would have very high resolution due to the large number of large and small baselines and I expect time synchronization would be an issue, but perhaps they could find a clever way to synchronize. The 1 meter dishes are small and so for the dish to have any relevance to the project the wavelength has to be a lot smaller....

4

As the Wikipedia page on VLBI interferometry points out, there have been a few spacecraft with radio antennae which have formed (along with ground based stations) part of radio interferometer networks. The examples given are the KRT 10-m dish on the Salyut space station, and the HALCA and Spektr-R satellites. The latter was in an orbit with an apogee almost ...

3

The blind spots are caused by the way the detectors work. They are sensitive to a gravitational wave (GW) changing the relative path length along interferometer arms at right angles to each other. Gravitational waves come in two polarisations (plus and cross). These polarisations cause alternate perpendicular expansions and contractions in space, but are ...

3

Yes it is possible that a cloud reduce the visibility because the matter in it will absorb some of the light which is going through. Yes, we cannot see all the universe and so we can see interstellar clouds up to a certain distance. Indeed, light takes time to reach us. If there is a star behind a cloud you will have difficulties to determine its true ...

3

So long as you accurately know the beam size, then yes multiplying your Jy/beam measurement (effectively flux density) by the beam size (effectively area of flux) will give you the total Jy (effectively the flux). See this source as an example.

3

This article basically seems to answer the question. They quote from an earlier study: "Although no CCSNe have currently been detected by gravitational-wave detectors, previous studies indicate that an advanced detector network may be sensitive to these sources out to the Large Magellanic Cloud (LMC). A CCSN would be an ideal multi-messenger source for ...

3

Is radar interferometry used, or feasible, for ground based astronomy? Yes it is! My answer to How can we install a radar on radio telescopes like FAST or GMRT? beings:;; The article is quite informative. It is a summary of "a paper published in the journal Scientia Sinica Information" which appears to be Discussion on the requirements and ...

3

They do use two or more detectors to triangulate the origin of a source. Most recently the Advanced Virgo detector in Italy was used in conjunction with the two LIGO detectors in the USA. This has been published in Physical Review Letters (Phys. Rev. Lett. 119, 141101 – Published 6 October 2017). With two detectors the sky area for "pinpointing" the source ...

3

A supplemental answer to probably someone's answer: Why this can indeed be called interferometry: Once one thinks in terms of physical optics (e.g. $\text{exp}(j(\omega t - \mathbf{k} \cdot \mathbf{r} ))$ ) instead of ray optics, imaging is always an interference problem, and the math behind correlating signals from an array of radio telescopes to produce ...

3

The SIMBAD link might be there just because Osterbrock's 2004 AAS presentation about the interferometer mentioned an observation of Betelgeuse. This would be consistent with the policy stated in Wenger et al. 2000: No assessment is made of the relevance of the citation in terms of astronomical contents: the paper can be entirely devoted to the ...

3

This is a brief and very general answer which points to some papers which deal with LIGO calibration in detail. More detailed answers might be possibly given on either point, but can easily cover complete books each easily, too. A response or transfer function of a piece of equipment describes how the device responds to an input signal. This could be in ...

3

This is answering a somewhat different question, but one that seems implied by this one: To put a radio telescope on Mars requires the capability to launch the radio telescope to Mars, and then to land it on Mars and then deploy it there. This will be considerably more costly and difficult than just launching it into solar orbit...after all, the first step ...

2

The reason you would want to cover most of your aperture is so you can point directly at a huge light source (i.e. a star), but ignore most of the light coming from it. This makes it easier to directly detect faint features around the source that would ordinarily be washed out by the light from the source itself (i.e. planets and the like). I believe this is ...

2

This would not be a giant version of eLISA, but a small (and complicated) one. The distance between the LISA satellites will be 1 million kilometers, while the moon is on average 380.000km from Earth. So that arm would be less than half as long. Geosynchronous orbit is at 36.000km, not even 10% of the distance to the moon. The difference in length between ...

2

As far as I know the only option here is numerical general relativity. There are no known exact solutions for the general two-body problem in GR, since the field equations are very non-linear. Even there there are limits, since when the fields get strong enough the bodies will start to deform in complex ways that also depend on the equation of state of the ...

2

The simple answer is that it isn't resolving in both orthogonal directions equally well. The horizontal dimension is the binocular dimension, and from looking at your animation, it looks to have about ~3 times the resolution. The horizontal banding, I'm pretty sure is not ringing, and is in fact, representative of additional information. This article does a ...

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