# Tag Info

12

The arms are $4\,\mathrm{km}\,\times\, 1.2\,\mathrm{m}$: From the LIGO webpage: The 1.2 m diameter beam tubes were created in 19-20 m-long segments, rolled into a tube with a continuous spiral weld. While a mathematically perfect cylinder will not collapse under pressure, any small imperfection in a real tube would allow it to buckle (a crushed vacuum ...

10

Several factors influence whether a source of gravitational waves at a certain distance is observable by a certain instrument. One way to compute the limit to the distance is explained in Abadie et al 2010 and is as follows: Distance. The amplitude of gravitational waves decreases roughly with the inverse of the luminosity distance $\propto D^{-1}$. So ...

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 ...

8

This web page -- "Here is why the Hubble Space Telescope only looked a few times at Venus (and why it looked at the Moon instead)" -- seems like a pretty good answer to your main question (note: "MAST" = Mukulski Archive for Space Telescopes): There are only a few times the Hubble Space Telescope did look to Venus according to MAST. ...

7

In principle, not much different to LIGO, since LIGO is sensitive to kHz gravitational waves. But you need to find ways to increase the sensitivity at kHz frequencies, without compromising response at lower frequencies, or perhaps having a tuneable response. These improvements are likely to come with increased laser power and developments in the optics and ...

7

I'm not familiar with the design of the ProjectBlue telescope, but I think you have answered your own question. The habitable zones for Alpha Cen A and B, are approximately centred at 1.25au and 0.7au. Both are at a distance of 4.37 light years. 1au at 4.37 light years, subtends an angle of 0.74 arcseconds. If working at blue wavelengths (the aim appears ...

7

My ad-hoc opinion: This wouldn't be the first step of Venus exploration. Geologic in-situ investigation of the resurfacing hypotheses would already be a very challenging mission. Might be, one could find some metamorphic remnants which have survived the last resurfacing, and one could determine the age of rocks. Might be there exist some old layers below the ...

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 ...

4

To briefly supplement Rob's answer, there is at least one concept being floated for a gravitational-wave detector which is explicitly targeting kilohertz gravitational waves and sacrificing sensitivity to lower frequencies: the Neutron Star Extreme Matter Observatory (NEMO). It is hoped that such an observatory would join the global network by the late 2020s ...

3

Here is my attempt to reconcile your calculations. If the AB g-band apparent magnitude is 22.5, then the flux density in the g-band is given by $$f_{\nu} = 10^{(-48.6-22.5)/2.5} = 3.63 \times 10^{-29}\ {\rm erg\ cm}^{-2} {\rm s}^{-1} {\rm Hz}^{-1}$$ If the distance is 1991 Mpc, then the absolute g magnitude is $$M_g = m_g - 5\log d + 5 = -19.0$$ The ...

3

Generally speaking as many as possible because the number of lenslets determines the lateral wavefront resolution. But in reality there are a few factors to be considered. Wavefront sensor Say your lenslet array is of focal length $f$ and subaperture size $D$, given a maximum desired detection angle $\alpha$ (in your case is $2'' \approx 1\times10^{-5}\, \... 3 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 Answers to What is the functional difference between DSB and 2SB mixers, and why exactly would 2SB be better for radio astronomy? in Signal ... 3 A month after I asked this question, Keck Institute for Space Studies kindly arranged three lectures uploaded June 12, 2014, to provide some good answers :-) Major science questions for Venus Jeffery Hall, JPL Options for a seismic investigation of Venus David Mimoun, ISAE Toulouse Exploring Venus with Landers, orbiters and ballons Dave Stevenson, Caltech ... 3 This construct was a telescope. Citing this article: Owing to the difficulty of erecting a double tower, most other astronomers follow the mechanically simpler plan of laying the camera tube horizontally and allowing the sunlight to be fed into it by means of a plane mirror driven by clockwork to counteract the westward motion of the sun.pg. 255 A ... 3 Yes, it is possible; see https://twitter.com/sevospace/status/1328082050889490433 However, M. Voltmer used a “custom-made sodium filter,” without giving any details… 3 As an addendum to Sexti Empirici answer note that LIGO and Virgo have not yet reached their full "design" sensitivity. Each run their sensitivity is further improved. The current observation run (O3) is already quite a bit more sensitive than the preceeding (O2) run. Some public alerts for candidate observations claim distances up to 6.5 Gpc. The next ... 3 You seem to have all the ingredients apart from the variables of what size your detector pixels are (either physically or binned in software/hardware) and the angular extent of the object you are taking a spectrum of. The basic trade-off, as you say, is between flux and spectral resolution, but there are limits to that trade off. You should not reduce your ... 3 I think this is largely a matter of what you decide is incremental as opposed to a generational change. The basic location and overall size and detection principle of the interferometers did not change. An important change to the interferometer configuration was the addition of the signal recycling mirror that allows a certain amount of "tuning" of ... 2 I don't feel that ProfRob's answer does the step to advanced LIGO justice. First, it is important to recognize that LIGO, from its inception, was envisioned as a two-stage project. From Caltech`s LIGO lab: ... and in 1989, Vogt, Drever, Fred Raab, Thorne and Weiss submitted a joint Caltech/MIT proposal for LIGO construction to the NSF.The proposal ... 2 Unless I've done my maths wrong, the period of total eclipse is about 18 seconds. The CHIMERA camera at Mt Palomar, the instrument which followed up the discovery of this system, can take exposures at up to 8 full 1k$\times\$1k frames/second and considerably higher if windowed on an object. There is no need for photon-counting equipment for such a slowly ...

2

The GREAT receiver attached to SOFIA to detect far-infrared radiation incorporates elements reminiscent of both radio and optical detectors, but since it works by mixing a signal from a tunable oscillator with the oscillating field from the incoming radiation rather than by the photoelectric effect as in most optical detectors, you might consider it more ...

2

There are two types of parallel observations: Coordinated Parallel and Pure Parallel. Coordinated Parallel means part of the same proposal, so it has to have the same scientific justification: you have to come up with a good case for why the different observations would be useful for the same project. (This is case with CANDELS.) Pure Parallel means ...

2

LIGO detectors have two 4 km arms, and everything in those arms in suspended in a vacuum. The actual dimensions of those arms I was unable to find, but the published paper here has more information for you to peruse.

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The feed horn is an antenna which has an antenna pattern Source However, not all feeds are horns. Here is an image of a parabolic dish with a Yagi feed: Source Ideally, you want the beam width of the horn antenna to cover the entire dish and only the dish. So if the beam width of the horn antenna is, say, 30 degrees, you want the dish to subtend 30 ...

1

This is a partial answer only. I'd expected that the Paywalled Geophysical Research Letter linked below would have some quantitative information on brightness, but once I got behind a paywall and looked at it I found it didn't and neither did any other paper I could find. I'll keep looking for some quantitative brightness information and update when I find ...

1

You're right to think that this is a calibration technique. In use here are laser combs that use self-interference of short pulses that are reflected multiple times inside their own cavity to generate the spacing that you see. The spacing then is mainly limited by the inverse of the pulse length, and thus by current laser technology. Sharpness of ...

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